Synthesis and experimental investigation of δ-MnO2/N-rGO nanocomposite for Li-O2 batteries applications

Abstract

Among all the electrocatalysts for Lithium-Air battery (Li-air), Platinum Pt is the best performing cathode material. However, the high cost of noble Pt metal and scarcity nature impedes the use of Pt-based catalysts from being extensivity used in commercial applications. Therefore, there is an urgent need to develop an efficient and cost-effective alternate electrocatalyst to replace Pt-based materials in lithium-oxygen (Li-O2) battaries. In the present work, δ-MnO2/N-rGO composite (MNGC) has been synthesized by a simple non-template hydrothermal approach. MNGC with a porous wall structure composed of ultrathin nanosheets exhibits excellent electrochemical properties for oxidation–reduction reaction (ORR). MNGC can provide numerous pathways for abundant oxygen and electrolyte access to facilitate the mass transfer of lithium-ion. Such a well-designed structure offers the right electrocatalyst for the air cathode in lithium-oxygen (Li-O2) battaries. The prepared samples principal characteristics are analyzed, which verified the successful synthesis of sheet-like δ-MnO2 grown over the surface of nitrogen-doped reduced graphene oxide (N-rGO). Linear sweep voltammetry (LSV) results of MNGC showed enhanced ORR performance compared to MnO2 and N-rGO in terms of the half-wave potential, limiting current, and onset potential. MNGC electrode displayed superior cyclic performances of Li-air with a stable specific capacity, decreased overpotential, reversibility, and rate capability. Li-O2 battery was also tested with MNGN electrode for limited discharge capacity of 500 mAh/g, long-term cycling was achieved without electrolyte degradation. A high specific capacity of 5250 mAh/g was obtained at a high current density of 0.2 mA/cm2. The interlinked effect of δ–MnO2 and N–rGO for supporting the electrochemical interaction between O2 and Li is explained for improved columbic and energy efficiency of Li–O2 battery