Reaction Mechanisms for Long-Life Rechargeable Zn/MnO₂ Batteries

Abstract

Rechargeable aqueous Zn-ion batteries (ZIBs) are very promising for large-scale grid energy storage applications owing to their low cost, environmentally benign constituents, excellent safety, and relatively high energy density. 1, 2 Their usage, however, is largely hampered by the fast capacity fade. The cycle stability seems to be highly rate-dependent, 3 which poses an additional challenge, but can also play a pivotal role in uncovering the reaction mechanisms. The complexity of the reactions has resulted in long-standing ambiguities of the chemical pathways of Zn/MnO2 system, and has led to many controversies with regard to their nature. In this report, we present a combined experimental and theoretical study of Zn/ MnO2 cells. We found that both H + /Zn 2+ intercalation and conversion reactions occur at different voltages, and that the rapid capacity fading can clearly be ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By avoiding the irreversible conversion reactions at ~ 1.26 V, we successfully demonstrate ultra-high power and long-life Zn/MnO2 cells which, after 1000 cycles, maintain an energy density of ~ 231 Wh kg-1 and ~ 105 Wh kg-1 at a power density of ~ 4 kW kg-1 (9C, ~ 3.1 A g-1) and ~ 15 kW kg-1 (30C, ~ 10.3 A g-1), respectively. The excellent cycle stability and power capability are superior to most reported ZIBs or even some lithium-ion batteries. The results establish accurate electrochemical reaction mechanisms and kinetics for Zn/MnO2, and identify the interplay of the voltage window and rate as the determining factors for achieving excellent cycle life. Broader Context The increasing interest and importance in large-scale grid storage technology are attributed to multiple factors, including managing peak demands, improving the grid reliability, integrating most sustainable energy sources such as solar radiation, wind, wave power, geothermal energy, etc., and further powering the energy infrastructures. Rechargeable aqueous Zn-ion batteries (ZIBs) with mild electrolytes have the advantages of low cost materials (Zn/ MnO2), manufacturing (air-and water-inert Zn anode), and recycling (mild electrolytes); relatively high energy density; and excellent safety, making them prospective candidates for large-scale grid storage. Their low cyclability, however, has remained a grand challenge, hindering the widespread applications of these attractive ZIBs. A prerequisite for improving the cycle life and electrochemical performance of Zn/MnO2 batteries is to accurately determine the reaction mechanisms, especially under different rates, which poses a considerable challenge. In our combined experimental and computational study, a concomitant intercalation and conversion reactions of H + /Zn 2+ occurring at different voltages in the Zn/MnO2 system is established. The rapid capacity fading is unambiguously ascribed to the rate-limiting and irreversible conversion reactions at a lower voltage. By mitigating or avoiding the irreversible conversion reactions at the lower ...

Electrodeposited Manganese Oxide on Carbon Paper for Zinc‐Ion Battery Cathodes

“…On subsequent cycling, two reduction peaks are present at 1.26 V and 1.37 V on the cathodic scan. Two oxidation peaks are also present during the anodic scan at 1.57 V and a small shoulder at ∼1.60 V. The CV results show relatively good overlap upon cycling and the CV behaviour is similar to that of other Mn oxide‐based ZIBs …”

“…With electrodeposition, the active cathode materials for ZIBs can be directly deposited onto an electrode substrate at room temperature without the requirement of binders and lengthy fabrication times. Electrodeposition has been utilized previously in the literature to fabricate Mn oxide cathode materials for ZIBs . Sun et al.…”

“…Li et al. utilized a galvanostatic method to deposit MnO 2 onto carbon electrodes with a battery electrolyte composed of 1 M ZnSO 4 and 0.2 M MnSO 4 …”

Unravelling H+/Zn2+ Synergistic Intercalation in a Novel Phase of Manganese Oxide for High‐Performance Aqueous Rechargeable Battery

“…Besides, to make the structural evolution of MON more clear, all electrodes are immersed in a distilled acetic acid to remove the Zn 4 SO 4 (OH) 6 (H 2 O) 5 on electrode surface, and the obtained XRD patterns are shown in Figure c. Only the characteristic peaks of MON can be observed, which is obviously different from that of previously reported species (e.g., spinel ZnMn 2 O 4 , MnOOH, and tunneled γ‐Zn x MnO 2 , and Zn‐buserite phase). The peaks of (100) and (11‐1) planes of MON show obvious shift toward smaller angles upon discharging, and then shift back upon charging, indicating a reversible lattice expansion and contraction process.…”

“…However, the structure collapse of MnO 2 (α‐, β‐, γ‐, etc.) upon cycling, due to a combined effect of Mn 2+ dissolution, phase conversion, collapse of layered structure, and formation of inactive by‐products, usually results in rapid capacity fading and then its practical application is restricted.…”