Reversible Multivalent (Monovalent, Divalent, Trivalent) Ion Insertion in Open Framework Materials

Abstract

The reversible electrochemical insertion of multivalent ions into materials has promising applications in many fi elds, including batteries, seawater desalination, element purifi cation, and wastewater treatment. However, fi nding materials that allow for the insertion of multivalent ions with fast kinetics and stable cycling has proven diffi cult because of strong electrostatic interactions between the highly charged insertion ions and atoms in the host framework.Here, an open framework nanomaterial, copper hexacyanoferrate, in the Prussian Blue family is presented that allows for the reversible insertion of a wide variety of monovalent, divalent, and trivalent ions (such as Rb + , Pb 2+ , Al 3+ , and Y 3+ ) in aqueous solution beyond that achieved in previous studies. Electrochemical measurements demonstrate the unprecedented kinetics of multivalent ion insertion associated with this material. Synchrotron X-ray diffraction experiments point toward a novel vacancy-mediated ion insertion mechanism that reduces electrostatic repulsion and helps to facilitate the observed rapid ion insertion. The results suggest a new approach to multi valent ion insertion that may help to advance the understanding of this complex phenomenon.

A Novel Superconcentrated Aqueous Electrolyte to Improve the Electrochemical Performance of Calcium-ion Batteries

“…Similar discrepancy has been reported in previous studies on the PBA electrode in aqueous electrolytes. 13,14 However, the reason for the discrepancy is not clear at present, and the detailed interpretation of this phenomenon is beyond the scope of the present work. The parts that we must notice in Figures 2a and 2b are the improved electrochemical performances in the superconcentrated electrolyte.…”

“…11,12 In such a case, an active material with large channels that allow the passage of hydrated polyvalent cations is necessary. Wang et al 13,14 observed that various polyvalent cations could rapidly diffuse into Prussian Blue analogue (PBA) electrodes, which contain large open interstitial sites (4.6 ¡ in diameter) and ©100ª channels (3.2 ¡ in diameter) in polyvalent cation-based aqueous electrolytes. However, the low charge/discharge capacities and capacity reduction during the initial cycles must be improved.…”

“…It is well known that the capacity reduction of an electrode containing transition metals is generally affected by the dissolution of the transition metal ions into the electrolyte. 13,14,2327 Therefore, the capacity reduction of the CuHCF electrode in the dilute electrolyte system might be affected by the dissolution of the copper or iron ions that exist in the CuHCF electrode; this dissolution phenomenon might be suppressed in the superconcentrated electrolyte owing to the presence of the highly concentrated Ca(NO 3 ) 2 salt. The other possibility is that, as previously mentioned, the hydrated calcium ions that exist in the dilute electrolyte have a bigger hydration radius than that of those present in the superconcentrated electrolyte.…”

A concentrated electrolyte for zinc hexacyanoferrate electrodes in aqueous rechargeable zinc-ion batteries

“…The capacity gradually increased during the initial cycles in both electrolytes. The reason for this phenomenon is unclear at present and a detailed interpretation is beyond the scope of this work, but it may be related to activation or conditioning effects [20,21,26].…”

“…In particular, PBAs are notable potential cathode materials for application in ARZIBs owing to their superior characteristics, such as structural stability, large channels, and ease of synthesis [9,18]. Additionally, these materials have large open sites (4.6 Å in diameter) and <100> channels (3.2 Å in diameter), which enable the rapid diffusion of various hydrated metal ions, including zinc ions [19][20][21]. However, the electrochemical performance of these materials has to be improved, as they exhibit relatively low capacities and capacity reduction during the initial cycles.…”