α-Fe2O3作为水相电池阳极的电荷储存行为和反应机理( Charge storage behavior and reaction mechanism of α-Fe2O3 as anodes for aqueous batteries - ScienceDirect )

PL A TL A JB Xu CA Shuang

α-Fe2O3 has been widely reported as negative electrodes in aqueous based energy storage systems. Yet, investigation on its electrochemical behavior and energy storage mechanism is still a desolate field, especially as anodes for batteries. Herein, ring-like α-Fe2O3 is synthesized and its charge storage behavior is explored in both neutral and alkaline electrolytes. The as-obtained samples exhibit high capacities with low negative charging/discharging plateaus but poor cycling performance. In Li2SO4, a reversible capacity of 90 mAh g at 1 A g is achieved, while it declines quickly to about zero at the first 20 cycles. In Na2SO4 and K2SO4 with larger cations, the initial capacities are lower and the decay speeds are faster, indicating a cation involved charge storage process. With careful analysis, it is proposed that part of Fe2O3 is reduced to be resoluble Fe followed by the formation of Fe(OH)2 around the electrode in low potential range owning to the insertion of (H3O), and subsequently converted into FeOOH as precipitation, which would cause irreversible mass loss and hence fast capacity decay. While in alkaline solution of LiOH, a higher reversible capacity of 160 mAh g at 1 A g is reached accompanied by better cycling performance and much higher Coulombic efficiency of 100%. Yet, the durability is still unsatisfied. With operando Raman, it is found that Fe2O3 is irreversibly reduced to be Fe3O4 during the discharging process. Structural collapse of Fe3O4 during the following cycles should take main responsibility for the poor durability. Hence, how to inhibit mass loss of Fe2O3 in neutral solution and structure collapse of Fe3O4 in alkaline solution is supposed to be effective strategy to enhance the stability of Fe2O3 based electrodes.

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