(Invited) Prussian Blue Analogues Materials for Energy Storage Applications

Abstract

The open framework structure of Prussian Blue analogues (PBAs) is fundamentally different from other insertion electrode materials because of its large channels and interstices1. This structure is composed of a face-centered cubic framework of transition metal cations where each cation is octahedrally coordinated to hexacyanometallate groups. Large interstitial “A Sites” within the structure can accommodate zeolitic water and hydrated alkali ions (see Figure). This results in a general chemical formula of AxPR(CN)6nH2O, where A is an alkali cation such as K+or Na+, P is a transition metal cation and R(CN)6is a hexacyanometallate anion. Both the P-site transition metal cation and the R(CN)6 3-hexacyanometallate anion can be electrochemically active in this structure. The Prussian Blue framework structure has wide channels between the A sites, allowing rapid insertion and removal of not only alkali ions but also divalent and trivalent ions from aqueous solutions2. In addition, there is little lattice strain during cycling because the A sites are larger than the hydrated ions that are inserted and removed from them. The result is an extremely stable and rapid electrode: thousands of deep discharge cycles and high capacity retention at high C-rates were demonstrated in aqueous electrolytes3,4 , 5. When operated in organic, Na-ion electrolytes they show high specific capacities, long cycle life and good rate capability6. In my talk, I will show how these exciting properties are linked to the peculiar crystal structure of PBAs and how their chemistry can be easily tuned to adapt their electrochemistry to a variety of energy storage applications. References Hurlbutt, K., Wheeler, S., Capone, I. & Pasta, M. Prussian Blue Analogs as Battery Materials. Joule 2, 1950–1960 (2018).Wang, R.Y. et al.Reversible Multivalent (Monovalent, Divalent, Trivalent) Ion Insertion in Open Framework Materials. Adv. Energy Mater.5, 1–10 (2015).Pasta, M. et al.Manganese–cobalt hexacyanoferrate cathodes for sodium-ion batteries. J. Mater. Chem. A4, 4211–4223 (2016).Pasta, M. et al.Full open-framework batteries for stationary energy storage. Nat. Commun.5, 3007 (2014).Wheeler, S., Capone, I., Day, S., Tang, C. & Pasta, M. Low-Potential Prussian Blue Analogues for Sodium-Ion Batteries: Manganese Hexacyanochromate. Chem. Mater., article ASAP (2019).Lee, H.W. et al.Manganese hexacyanomanganate open framework as a high-capacity positive electrode material for sodium-ion batteries. Nat. Commun.5, 5280 (2014). Figure 1