Progress in Rechargeable Aqueous Zinc‐ and Aluminum‐Ion Battery Electrodes: Challenges and Outlook

Abstract

www.advsustainsys.comion-based chemistries exclusively. Though few reviews document electrode materials and their performances for rechargeable aqueous Zn-and Al-ion batteries, [23,[25][26][27] a comprehensive understanding of ion storage mechanisms remains poorly enunciated. We believe the key to successful implementation of MV-ion batteries requires a simultaneous understanding of various elemental chemistries, in context with each other. Here, we summarize reported electrochemical reactions for Zn-ion and Al-ion electrodes. We compare activation mechanisms for ion transport and the role of water in various crystal lattices, and analyze specific challenges for electrode materials such as limited cation mobility, spontaneous dissolution, poor cycling, O 2 interaction, untoward proton/hydronium coinsertion, ineffective electrode-electrolyte interface formation, and current-collector corrosion. We illustrate how these challenges are dependent on some of the battery design parameters, with an aim to find optimized solutions or alternative strategies to increase the viability of Zn-ion aqueous batteries (ZIABs) and Al-ion aqueous batteries (AIABs) in BESS. Aqueous Rechargeable Electrodes for Zn-Ion StorageIn this review, we discuss rechargeable electrodes which can insert Zn 2+ ions. Since, electrodes for zinc-nickel batteries, [28,29] alkaline Zn-MnO 2 batteries, [30,31] or the hybrid zinc aqueous batteries, [32] store other ions (and not Zn 2+ ), we do not discuss these systems here. Majority of the literature for ZIAB electrodes spans various polymorphs of manganese dioxide, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] vanadium compounds, [49][50][51][52][53][54][55][56][57][58][59][60][61] and hexacyanoferrates, [62][63][64][65] and we discuss few Zn 2+ storage mechanisms for these electrodes. Additionally, we also highlight key similarities, missing links in the reaction mechanism, and the role of water, if any. 2.

Flexible Zn‐Ion Batteries: Recent Progresses and Challenges

“…iii) Radius of Zn 2+ . Zn 2+ can tightly coordinate with water to form hydrated Zn 2+ ([Zn(H 2 O) 6 ] 2+ ), which inserted into the host cathode in different ways . When the ion‐channel size is not large enough to accommodate the hydrated Zn 2+ , desolvation could happen for the successful cation intercalation …”

Flexible Zn‐ion batteries based on manganese oxides: Progress and prospect

“…In tetragonal λ‐MnO 2 , Zn 2+ diffuses from 8a‐sites to neighboring 8a‐sites through 16c‐sites; however, Mn atoms at 16d‐sites (close to 16c‐sites) hinder the movement of Zn 2+ by electrostatic repulsion 81 . These findings confirm that further architecture modification is necessary for spinel‐type samples like λ‐MnO 2 and ZnMn 2 O 4 to become qualified Zn 2+ hosts considering their limited 3D tunnels and strong electrostatic repulsion toward Zn 2+ 26,38,39,48,67 . As shown in Figure 6, a treatment on the ZnMn 2 O 4 lattice was carried out to produce Mn vacancies or deficiencies by extracting oxygen anions, which lowers the electrostatic barrier for Zn 2+ transfer and alleviates the Mn species dissolution due to the higher Mn oxidation state.…”

Intercalated water in aqueous batteries

“…The basic reason lies in the dissolution of Mn 2+ into the aqueous electrolyte, which leads to a change of stoichiometry and potential lattice rearrangement. Figure 3A shows the structure of an α‐MnO 2 , which has a 2 × 2 tunnel structure with corner‐sharing MnO 6 octahedra 34 . By comparing the XRD patterns of a Zn 2+ ‐intercalated α‐MnO 2 , Lee et al 43 found that the structure turned into a birnessite‐MnO 2 , which is similar with α‐MnO 2 except that the α‐MnO 2 layers are disconnected by one octahedral vacancy and are separated by two vertically aligned MnO 6 octahedra.…”