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Critical Role of pH Evolution of Electrolyte in the Reaction Mechanism for Rechargeable Zinc Batteries
Author(s) -
Lee Boeun,
Seo Hyo Ree,
Lee Hae Ri,
Yoon Chong Seung,
Kim Jong Hak,
Chung Kyung Yoon,
Cho Byung Won,
Oh Si Hyoung
Publication year - 2016
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201600702
Subject(s) - electrolyte , zinc hydroxide , inorganic chemistry , chemistry , zinc , manganese , dissolution , hydroxide , electrochemistry , battery (electricity) , lithium hydroxide , reaction mechanism , sulfate , ion , electrode , ion exchange , catalysis , organic chemistry , power (physics) , physics , quantum mechanics
The reaction mechanism of α‐MnO 2 having 2×2 tunnel structure with zinc ions in a zinc rechargeable battery, employing an aqueous zinc sulfate electrolyte, was investigated by in situ monitoring structural changes and water chemistry alterations during the reaction. Contrary to the conventional belief that zinc ions intercalate into the tunnels of α‐MnO 2 , we reveal that they actually precipitate in the form of layered zinc hydroxide sulfate (Zn 4 (OH) 6 (SO 4 )⋅5 H 2 O) on the α‐MnO 2 surface. This precipitation occurs because unstable trivalent manganese disproportionates and is dissolved in the electrolyte during the discharge process, resulting in a gradual increase in the pH value of the electrolyte. This causes zinc hydroxide sulfate to crystallize from the electrolyte on the electrode surface. During the charge process, the pH value of the electrolyte decreases due to recombination of manganese on the cathode, leading to dissolution of zinc hydroxide sulfate back into the electrolyte. An analogous phenomenon is also observed in todorokite, a manganese dioxide polymorph with 3×3 tunnel structure that is an indication for the critical role of pH changes of the electrolyte in the reaction mechanism of this battery system.