New types of energy storage are needed in conjunction with the deployment of renewable energy sources and their integration with the electrical grid. We have recently introduced a family of cathodes involving the reversible insertion of cations into materials with the Prussian Blue open-framework crystal structure. Here we report a newly developed manganese hexacyanomanganate open-framework anode that has the same crystal structure. By combining it with the previously reported copper hexacyanoferrate cathode we demonstrate a safe, fast, inexpensive, long-cycle life aqueous electrolyte battery, which involves the insertion of sodium ions. This high rate, high efficiency cell shows a 96.7% round trip energy efficiency when cycled at a 5C rate and an 84.2% energy efficiency at a 50C rate. There is no measurable capacity loss after 1,000 deep-discharge cycles. Bulk quantities of the electrode materials can be produced by a room temperature chemical synthesis from earth-abundant precursors.

This new type of safe, fast, inexpensive, long-cycle life aqueous electrolyte battery relies on the insertion of sodium ions into the copper hexacyanoferrate (CuII—N≡C—FeIII/II) cathode and a newly developed manganese hexacyanomanganate (MnII—N≡C—MnIII/II) anode, each of which have the same open framework crystal structure.

Nature Communications 5, Article number: 3007 doi:10.1038/ncomms4007, Published 06 January 2014

http://www.nature.com/ncomms/2014/140106/ncomms4007/full/ncomms4007.html