adaptability for homes, communities, and the grid. [4,5] Although non-aqueous lithium-ion batteries (LIBs) are the technology of choice for electromobility, cost and safety issues caused by the flammable and volatile organic electrolyte hinder their wide application in large-scale stationary applications, [6] in which cost and safety are the determining factors instead of energy density. [7] In this context, rechargeable aqueous batteries, which use non-flammable and less-volatile aqueous electrolytes become appealing alternatives for large-scale stationary applications. [8,9] The first aqueous battery based on LiMn 2 O 4 //VO 2 , featuring a "rocking-chair" mechanism was proposed by Dahn's and co-workers in 1994. [10] The limited electrochemical window of aqueous electrolytes was extended in 2015 by using a "waterin-salt" electrolyte designed by Wang's group, demonstrating a LiMn 2 O 4 //Mo 6 S 8 aqueous LIB with a high output potential of 2.3 V. [11] Beyond aqueous LIBs, other aqueous chemistries based on alternative metallic cations, that is, Na + , [12][13][14] K + , [15,16] Zn 2+ , [17][18][19] Mg 2+ , [20,21] Ca 2+[22] and Al 3+ , [23] are currently being intensively investigated. Alongside, aqueous ammonium-ion batteries (AAIBs) using non-metallic NH 4 + are gradually emerging, driven by the NH 4 + fast diffusion kinetics. [24,25] Indeed, NH 4 + possesses a small hydrated ionic radius (3.31 Å) providing fast diffusion kinetics. [26] Despite some pioneering works [24,27] have demonstrated the potential of this battery chemistry, it is still very challenging to develop a stable full "rocking-chair" AAIB with high coulombic efficiency, due to the instability of electrode materials in the present diluted aqueous electrolytes.To address the above-mentioned challenge, two main strategies can be adopted. The first is to develop novel and stable electrode materials. Among the so far proposed electrode materials, the cost-efficient Prussian blue and its analogues (PBA), owing an open framework and large interstitial sites, have been intensively researched. [28][29][30] In addition, several inorganic materials including Ti 3 C 2 MXenes, [27] V 2 O 5 , [31] TiO 1.85 (OH) 0.30 •0.28H 2 O, [32] Fe 5 V 15 O 39 (OH) 9 •9H 2 O, [33] MoO 3 , [34] VS 2 /VO x , [35] NH 4 V 4 O 10, [36] MnO x , [37,38] as well as organic compounds such as 3,4,9,10-perylene tetracarboxylic diimide (PTCDI), [24] 1,4,5,8-naphthalene tetracarboxylic dianhydride-derived polyimide (PNTCDA), [39] polyaniline [40] and covalent organic frameworks (COFs) [41] have been investigated.
Rechargeable aqueous batteriesare promising devices for large-scale energy-storage applications because of their low-cost, inherent safety, and environmental friendliness. Among them, aqueous ammonium-ion (NH 4 + ) batteries (AAIB) are currently emerging owing to the fast diffusion kinetics of NH 4 + . Nevertheless, it is still a challenge to obtain stable AAIB with relatively high output potential, considering the instability of many electrode materials in an aqueous envi...