New Insights into Phase‐Mechanism Relationship of Mg_xMnO₂ Nanowires in Aqueous Zinc‐Ion Batteries

Abstract

In response to the call for safer energy storage systems, rechargeable aqueous manganese‐based zinc‐ion (Zn‐ion) batteries using mild electrolyte have attracted extensive attention. However, the charge‐storage mechanism and structure change of manganese‐based cathode remain controversial topics. Herein, a systematic study to understand the electrochemical behavior and charge storage mechanism based on a 3 × 3 tunnel‐structured MgxMnO2 as well as the correspondence between different tunnel structures and reaction mechanisms are reported. The energy storage mechanism of the different tunnel structure is surface faradaic dissolution/deposition coupled with an intercalation mechanism of cations in aqueous electrolyte, which is confirmed by in situ X‐ray diffraction, in situ Raman and ex situ extended X‐ray absorption fine structure. The deposition process at the cathode is partially reversible due to the accumulation of a birnessite layer on the surface. Compared to smaller tunnels, the 3 × 3 tunnel structure is more conducive to deposit new active materials from the electrolyte. Therefore, pristine MgxMnO2 nanowires with large tunnels display an excellent cycling performance. This work sheds light on the relationship between the tunnel structure and Mn2+ deposition and provides a promising cathode material design for aqueous Zn‐ion batteries.

Protocol in Evaluating Capacity of Zn–Mn Aqueous Batteries: A Clue of pH

“…[7,13] In the meantime, it brings up a disturbance to the charge-discharge behavior. For example, various unusual fluctuation phenomena caused by Mn 2+ additive have been observed, including unnatural increase, [13,35] attenuation, [15,16,22] combined fluctuation, [19,[36][37][38] and perfectly smooth trend of the cyclic curve (Figure 1a). [39][40][41] In most reports, a single electrochemical reaction process is declared in the whole cycle calendar.…”

“…The combinatory or preferential electrochemical behavior, including H + /Zn 2+ -dominated and Mn 2+ -dominated fluctuations, are prevalent in the reported ZMABs at near-neutral electrolytes. [8,9,[13][14][15][17][18][19][20]22,23,26,27,[35][36][37][39][40][41]48,65,66,68,[72][73][74][75] In particular, the H + /Zn 2+ -dominated electrochemical behavior with a flat or mildly ascending characteristics usually exhibits low Mn contribution (𝜖 < 50%). Such a system can be identified as cathodeleading ZMABs, of which the Mn 2+ -dominated region is generally absent or very short.…”

Electrodeposited Layered Sodium Vanadyl Phosphate (NaxVOPO4·nH2O) as Cathode Material for Aqueous Rechargeable Zinc Metal Batteries

“…A similar charge storage process is well known in the other cathode materials previously reported for ARZMBs. 60,61 The GCD analysis of the Zn∥fTCF/VP-200 cell is performed at various current rates ranging from 0.033 A g −1 (≈0.4 C) to 0.333 A g −1 (≈4 C). At a current rate of 0.033 A g −1 , the cell delivers a maximum specific discharge capacity of 100 mA h g −1 (equivalent to an areal capacity of 0.3 mA h cm −2 ), as shown in Figure 4b.…”

Unveiling the reaction mechanism of capacity reactivation in silver vanadate cathodes for aqueous zinc-ion batteries

“…[1][2][3][4] In this regard, aqueous zinc-ion batteries (ZIBs) have recently received attention due to their intrinsic advantages, including high safety, low cost, and environmental friendliness. [5][6][7][8][9][10] Different types of cathode materials, including manganese oxides, [11][12][13][14][15] vanadium oxides, [16][17][18][19][20][21] Prussian blue analogs, [22][23][24] and even organic cathodes, [25][26][27] have been widely utilized in the ZIBs, among which, vanadate-based cathodes, especially V 2 O 5 -originated species, have been extensively studied. Specically, because of the multivalent property, the open layered structure, and the support from the intercalated cations, V 2 O 5 -based materials can store more Zn 2+ to provide higher capacity.…”