Simultaneous Elucidation of Solid and Solution Manganese Environments via Multiphase Operando Extended X-ray Absorption Fine Structure Spectroscopy in Aqueous Zn/MnO₂ Batteries

Abstract

Aqueous Zn/MnO2 batteries (AZMOB) with mildly acidic electrolytes hold promise as potential green grid-level energy storage solutions for clean power generation. Mechanistic understanding is critical to advance capacity retention needed by the application but is complex due to the evolution of the cathode solid phases and the presence of dissolved manganese in the electrolyte due to a dissolution–deposition redox process. This work introduces operando multiphase extended X-ray absorption fine structure (EXAFS) analysis enabling simultaneous characterization of both aqueous and solid phases involved in the Mn redox reactions. The methodology was successfully conducted in multiple electrolytes (ZnSO4, Zn(CF3SO3)2, and Zn(CH3COO)2) revealing similar manganese coordination environments but quantitative differences in distribution of Mnn+ species in the solid and solution phases. Complementary Raman spectroscopy was utilized to identify the less crystalline Mn-containing products formed under charge at the cathodes. This was further augmented by transmission electron microscopy (TEM) to reveal the morphology and surface condition of the deposited solids. The results demonstrate an effective approach for bulk-level characterization of poorly crystalline multiphase solids while simultaneously gaining insight into the dissolved transition-metal species in solution. This work provides demonstration of a useful approach toward gaining insight into complex electrochemical mechanisms where both solid state and dissolved active materials are important contributors to redox activity.

Chrysanthemum-like Polyaniline-Anchored PANI0.22·V2O5·0.88H2O-Hybridized Cathode for High-Stable Aqueous Zinc-Ion Batteries

“…The b values for the oxidation (peaks 1, 2) and reduction (peaks 3, 4) are calculated to be 0.87, 0.95, 0.87, and 0.88, respectively (Figure b). These results suggested that the charge storage behavior in the P-60-120 °C electrode is controlled by a hybrid mechanism of ion diffusion process and surface capacitive response . Moreover, the reversible capacity contributions of the P-60-120 °C electrode at different scanning rates could be quantitatively evaluated based on the eq , , i = k 1 v + k 2 v 1 / 2 where k 1 and k 2 are constants at specific scanning rates.…”

“…These results suggested that the charge storage behavior in the P-60-120 °C electrode is controlled by a hybrid mechanism of ion diffusion process and surface capacitive response. 21 Moreover, the reversible capacity contributions of the P-60-120 °C electrode at different scanning rates could be quantitatively evaluated based on the eq 2, 40,47…”

“…To tackle these problems, a series of guest ions/molecules preintercalated in V-based oxide materials are proposed to stabilize their crystal frameworks and enlarge the interlayer spacing for facile Zn 2+ diffusion. However, most hetero ions are redox inactive and are liable to be extracted irreversibly during the repeat discharge processes, which will be at the expense of the overall reversible capacity of the materials. − Recent investigations demonstrate that introducing conductive organic small molecules [poly­(3,4-ethylene dioxythiophene), polyaniline, etc. ] to the interlayer of layered oxides allows for interlayer regulation and stabilizing structures via forming hydrogen bonds between the −NH 2 group and the V–O layer. − However, most of the so-called preinserted hydrated V 2 O 5 materials exhibit 2D belt-like or sheet-like architectures with relatively low specific surface areas.…”

Rational Design of Flexible Zn-Based Batteries for Wearable Electronic Devices

“…Figure a provides a classical example of σ-MnO 2 tunnels, where Zn 2+ is stripped out from a Zn metal anode during the discharging process and travels to intercalate into the layered structure in the charging process. Another cointercalation mechanism for the system with a special cathode has also been reported in recent publications, where Zn 2+ cointercalates with H + or H 2 O and is embedded in the cathode substrate in the form of hydrate or hydroxide . In general, the cathode in ZIBs based on the intercalation mechanism has an open structure: i.e., a specially designed ion storage host and layered ion transportation tunnel that allows facile insertion of Zn ions (eq ).…”

“…Another cointercalation mechanism for the system with a special cathode has also been reported in recent publications, where Zn 2+ cointercalates with H + or H 2 O and is embedded in the cathode substrate in the form of hydrate or hydroxide. 103 In general, the cathode in ZIBs based on the intercalation mechanism has an open structure: i.e., a specially designed ion storage host and layered ion transportation tunnel that allows facile insertion of Zn ions (eq 2).…”