Facile Synthesis of Porous Hollow Cobalt‐Doped λ‐MnO2 Nano Architectures as a High‐performance Anode Material for Li‐ion Batteries and Li‐ion Hybrid Supercapacitors

Abstract The cost‐effectiveness and easy availability of MnO 2 have attracted researchers′ attention as an anode electrode for LIBs over other transition metal oxides. However, MnO 2 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 MnO 2 , λ‐MnO 2 , due to its 3D spinel structure, can be applied in many applications. Usually, λ‐MnO 2 can be obtained by extracting lithium from LiMn 2 O 4 using complex electrochemical or acid leaching methods. This study presents a modified Li 2 O 2 assisted method to obtain cobalt‐doped 3D architectures of λ‐MnO 2 porous hollow nanostructures. The resultant Mn x Co 1‐x O y 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 MnO 2 anodes reported to date. Also, a LiHSC device is fabricated with Mn x Co 1‐x O y 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.