However, the above understanding is true only in certain circumstances. Despite being studied extensively, the reaction pathway of γ-MnO2 reduction still remains unclear, especially in the second electron region. Factors such as electrode conductivity, porosity, accessibility to electrolyte, and product solubility can significantly affect its discharge performance. In this presentation, the cycling performance of a γ-MnO2 electrode is studied both galvanostatically and potentiostatically. Its phase change during cycling is characterized by X-ray diffraction. It is found that with a good conductive carbon matrix and a highly porous structure, hausmannite is not formed during the first discharge cycle. In the absence of zincate ions, which is realized by applying a Zn-blocking separator 3,4, the achievable capacity of a Zn| γ-MnO2 primary battery is almost doubled, with a potential plateau around 0.95V, which is characteristic of the second electron reduction of γ-MnO2. The energy density achieved above 0.8V is increased by more than 50% (Figure 1). It is also found that the spinel phase materials are rechargeable with this highly conductive and porous electrode structure. A capacity close to 300 mAh/g-MnO2 can be delivered from both materials, suggesting that hetaerolite and hausmannite are not necessarily irreversible materials in a battery, which further provides more pathways for accessing the second electron capacity of MnO2.
References:
[1] Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S., Nat. Commun., 2017, 8, 14424
[2] Yadav, G. G.; Wei, X.; Huang, J.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Secor, J.; Banerjee, S., J. Mater. Chem. A, 2017, 5 (30), 15845-15854
[3] Huang, J.; Yadav, G. G.; Gallaway, J. W.; Wei, X.; Nyce, M.; Banerjee, S., Electrochemistry Communications 2017, 81, 136-140
[4] Huang, J.; Yadav, G. G.; Turney, D.; Nyce, M.; Banerjee, S., ECS Meeting, Abstract MA2018-01 115