Low-Potential Prussian Blue Analogues for Sodium-Ion Batteries: Manganese Hexacyanochromate

Abstract

Prussian blue analogues (PBAs) have recently shown outstanding electrochemical properties ascribable to their unique open-framework crystal structure that allows the reversible insertion of alkali ions with negligible perturbation to the framework itself. Many hexacyanoferrate materials have shown excellent properties and are some of the most promising sodium-and potassiumion cathode materials in both aqueous and organic electrolytes. However, there is a distinct lack of candidate PBA materials that operate at low potentials as their characteristic crystalline framework shows instability. In this article we characterise the structure and electrochemical behavior of manganese hexacyanochromate which exhibits reversible sodium insertion at-0.86 V vs. SHE (1.84 V vs. Na + /Na), whilst maintaining the characteristic PBA cubic structure. This is the lowest redox potential of reported PBA materials and shows fast kinetics in a high voltage water-in-salt electrolyte. Further reduction in potential in an organic electrolyte shows decomposition of the crystalline structure

Hexacyanoferrate‐Type Prussian Blue Analogs: Principles and Advances Toward High‐Performance Sodium and Potassium Ion Batteries

“…Among various subgroups of PBAs, hexacyanoferrates (HCFs, M ′ = Fe) are the most interested battery materials due to their high redox potential, ecofriendly synthesis and the low costs of raw materials, which are used as cathode materials. PBA‐type anode materials are very limited, which are based on other subgroups with M ′ = V, [ 12 ] Cr, [ 13,14 ] Mn, [ 15,16 ] and Co. [ 17 ]…”

Titanium Activation in Prussian Blue Based Electrodes for Na-ion Batteries: A Synthesis and Electrochemical Study

“…The presence of not only high-but also low-voltage plateaus has contributed in the past few years to the development of cathode and anode materials based on PBAs [25]. Indeed, hexacyanomanganates (AM[Mn(CN) 6 ]) [26,27], hexacyanocobaltates (AM[Co(CN) 6 ]) [28], and hexacyanochromates (AM[Cr(CN) 6 ]) [29] are reported as anode materials, displaying high reversible capacity at low potential (1.8 V vs. Na + /Na and~1.5 V vs. Li + /Li in organic electrolyte, −0.86 V vs. SHE(standard hydrogen electrode) in aqueous solution).…”

Filling vacancies in a Prussian blue analogue using mechanochemical post-synthetic modification

“…4 Increasing energy density therefore requires synthetic routes that minimise vacancies. 7 Traditional PBA synthesis routes usually yield samples with nominal compositions M[M 0 (CN) 6 ] 2/3 & 1/3 ÁxH 2 O (here M and M 0 are di-and trivalent transition-metal cations, respectively, and the symbol & represents a M 0 -site vacancy). 8 The corresponding structure is based on the simple cubic lattice; M 2+ and [M 0 (CN) 6 ] 3À species decorate alternate sites with one third of the hexacyanometallate sites occupied by coordinated and zeolitic water [ Fig.…”

“…Our focus is on Mn and Co compositions, since ICP analysis of K content is notoriously unreliable. 7 We infer K content on the basis of charge-balance. For the as-prepared sample, f = 0.700 (17), which suggests the initial composition was K 0.…”