Viable Synthesis of Porous MnCo2O4/Graphene Composite by Sonochemical Grafting: A High‐Rate‐Capable Oxygen Cathode for Li–O2 Batteries

• Published in: Chemistry : a European journal Vol. 24; no. 65; pp. 17303 - 17310
• Main Authors: Karkera, Guruprakash, Chandrappa, Shivaraju Guddehalli, Prakash, Annigere S.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 22.11.2018
• Subjects: Batteries; Catalysts; Cathodes; Chemical evolution; Chemical synthesis; Chemistry; Electric vehicles; Electrode materials; Graphene; highly porous cathodes; Kinetics; Li–O2 batteries; Nanospheres; Organic chemistry; Oxygen; porosity; Reaction kinetics; sonochemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201803569

With an anticipation of their use in electric vehicles, Li–O2 batteries are found to be attractive despite their complex chemistry and drawbacks. To be successful, cathode materials that are robust enough to overcome the sluggish kinetics of the charge–discharge reactions are essential. This work reports sonochemically synthesized porous MnCo2O4/graphene (MCO/G) as a hybrid cathode material in nonaqueous Li–O2 batteries. The MCO/G hybrid is synthesized in less than four hours and offers a strong synergistic coupling between the MnCo2O4 nanospheres and graphene sheets. It catalyzes the oxygen reduction through a three‐electron‐transfer process and initiates the oxygen evolution at 1.55 V vs. RHE in basic medium. A small charge–discharge voltage hysteresis of 0.8 V and a cycle life of 250 cycles at a limited capacity of 1000 mAh g−1 in a tetraglyme‐based nonaqueous Li–O2 battery is demonstrated. The porous channels created on the sonochemically synthesized cathode facilitates easy oxygen adsorption onto the active sites to accommodate more discharge products following its decomposition. It exhibits a better rate capability in comparison to the widely used Vulcan carbon and benchmark Pt/C catalysts. The excellent cyclability, rate capability, and low overpotential demonstrates MnCo2O4/graphene composite as a promising cathode candidate for Li–O2 batteries. The porous nanosphere architecture with internal oxygen diffusion pathways and peripheral conductive graphene extensions fulfils the requirements that a robust cathode is expected to have to overcome the harsh Li–O2 battery conditions and to serve as a high‐rate‐capable cathode for Li–O2 batteries. A highly porous MnCo2O4/graphene (MCO/G) hybrid with internal oxygen diffusion pathways has been developed by a sonochemical method. The porous channels throughout the bulk of the MCO nanospheres provide the added surface area that is required to attain the larger capacity. The MCO/G hybrid facilitates the reversible formation of Li oxides at lower overpotentials and higher rates in comparison to Pt/C and Vulcan carbon (see figure).