Accessing the second electron capacity of MnO2 by exploring complexation and intercalation reactions in energy dense alkaline batteries

• Published in: International journal of hydrogen energy 2018-04, Vol.43 (17), p.8480-8487
• Main Authors: Yadav, Gautam G., Wei, Xia, Huang, Jinchao, Turney, Damon, Nyce, Michael, Banerjee, Sanjoy
• Format: Article
• Language: English
• Subjects: 08 HYDROGEN; Alkaline; Batteries; Manganese dioxide; Zinc
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2018.03.061

MnO2 is one of the safest and most abundant electrochemical materials available. It exhibits polymorphism, which has been exploited in many applications especially batteries. In alkaline batteries, γ-MnO2 is widely used because its proton insertion reaction yields one e− (1st) per Mn at high voltages. It also gives a second (2nd) e− during dissolution-precipitation reactions that occur at lower voltages than the proton insertion; however, these 2nd e− reactions are highly irreversible. In this communication, we explore the reversibility of the 2nd e− reactions with bismuth oxide (Bi2O3) and copper (Cu) additives, and cycling in specific potential regions where δ-MnO2 is the polymorph synthesized electrochemically in-situ from γ-MnO2. The use of Bi2O3 and Cu add complexation and intercalation reactions, where presence and/or electrochemical activation of both are essential for reversibility and for capacity retention (50–100%). Attaining 300–610Wh kg−1 against a zinc anode is possible for these batteries, which could promote its use for many applications. [Display omitted] •Cycling potentials affect reversibility of MnO2 with Bi2O3 and Cu.•Complexation reactions take place even when activation potentials are not reached.•Cu as a lone additive unlocks high capacity retention and reversibility of MnO2.•Cu and Bi2O3 together allow for rapid attainment of MnO2's theoretical capacity.•Attaining 300–610Wh.kg−1 against a Zn anode is possible with additives.