Mechanistic investigation of redox processes in Zn–MnO₂ battery in mild aqueous electrolytes

Abstract

Zinc-MnO2 based batteries have acquired attention for grid-level applications, due to impressive theoretical performance, cost effectiveness and intrinsic safety. However, there are still many challenges that remain elusive due to...

Decoupling the Dynamics of Zinc Hydroxide Sulfate Precipitation/Dissolution in Aqueous Zn–MnO2 Batteries by Operando Optical Microscopy: A Missing Piece of the Mechanistic Puzzle

“…As in most previous works, two plateaus are observed during charge and discharge. These plateaus were often attributed to Zn 2+ insertion/extraction into/out of MnO 2 , [10][11][12][13][14][15][16][17][18][19][20] H + insertion/ extraction, [21][22][23][24] but they could also reveal MnO 2 electrodissolution/electrodeposition, [25][26][27][28][29][30][31][32][33] or combinations of the latter phenomena. [27,[34][35][36][37][38][39][40] From the point of view of the electrode material, most studies discuss complex composites of carbon and chemically synthesized MnO 2 particles of a specific phase (e.g., α-MnO 2 , β-MnO 2 , λ-MnO 2 …).…”

“…Therefore, it is practically blind to electrodeposited MnO 2 , which exhibits only short-range order, [41,42] as well as to potential amorphous precipitates. This is problematic as zinc hydroxides such as Zn 4 (OH) 6 SO 4 .xH 2 O (ZHS), which are expected to precipitate upon MnO 2 electrodissolution (see Equations 1 and 2) or H + insertion, [21][22][23][24][25]31,32,43] might not always appear in a crystalline form, thus hindering a comprehensive mechanistic analysis. Moreover, the temporal resolution of laboratory XRD (or spectroscopic techniques) might not be high enough to probe the competing dynamics of MnO 2 electrodissolution and ZHS precipitation.…”

Improvement of structural stability of cathode by manganese additive in electrolyte for zinc‐ion batteries

“…[15][16][17] The Zn 2+ -insertion-induced phase change and the following collapse of the structure of the MnO 2 cathodes, which result in low-rate capability and poor cycling stability, have limited the use of ZIBs. [15][16][17] Notably, for high-performance ZIBs, a judicious choice of an appropriate electrolyte with an additive is as important as identifying a promising cathode. While the addition of Mn 2+ salt has been proposed to prevent Mn dissolution, the underlying interaction between the cathode and electrolyte remains unclear.…”

“…9,13,14 Unfortunately, all MnO 2 cathodes show rapid capacity fading during repeated cycles, which has been reported to be caused by the dissolution of Mn (Jahn-Teller distortion) in the electrolyte. [15][16][17] The Zn 2+ -insertion-induced phase change and the following collapse of the structure of the MnO 2 cathodes, which result in low-rate capability and poor cycling stability, have limited the use of ZIBs. [15][16][17] Notably, for high-performance ZIBs, a judicious choice of an appropriate electrolyte with an additive is as important as identifying a promising cathode.…”

“…When an MnO 2 cathode is used, zinc sulfate (ZnSO 4 )‐based mild acidic electrolytes are preferred over alkaline electrolytes owing to their high reversibility and high stability 9,13,14 . Unfortunately, all MnO 2 cathodes show rapid capacity fading during repeated cycles, which has been reported to be caused by the dissolution of Mn (Jahn‐Teller distortion) in the electrolyte 15‐17 . The Zn 2+ ‐insertion‐induced phase change and the following collapse of the structure of the MnO 2 cathodes, which result in low‐rate capability and poor cycling stability, have limited the use of ZIBs 15‐17 .…”