Composite Prussian Blue Analogues Utilized As Cathode Materials in a Sodium Ion Battery

Increased environmental pollution and the inherent reliance of foreign import for fossil fuels and lithium have made the need for research towards alternative electrical energy storage systems. In this context, research in sodium ion batteries (NIBs) has become more prevalent since the price in lithium has increased due to its demand and reserve location.  Sodium is an abundant resource that is low cost and safe which makes it an attractive alternative to lithium. Its chemical properties are similar to that of Li which makes the transition into using Na chemistry for ion battery systems feasible.

In light of the requirements for grid scale energy storage: ultra-long cycle life (>20,000 cycles and calendar life of 15 to 20 years), high round trip efficiency (>90%), low cost, sufficient power capability, and safety, the need for a suitable cathode material with excellent capacity retention such as Na₂MnFe(CN)₆/K₂MnFe(CN)₆ composite will be investigated. Prussian blue (A[Fe^IIIFe^II (CN)₆], A=Na⁺ or K⁺) and its analogues have been investigated as alkali ion hosts for use as a cathode material. They have a cubic face-centered structure in which two different metal centers Fe³⁺ and Fe²⁺ are bridged by C≡N^- groups which provides large ionic channels along the <100> direction enabling facile insertion and extraction of alkali ions.  This material is also capable of more than one Na ion insertion per unit formula which holds great promise in increasing the energy density of the NIB. Electrochemical impedance spectroscopy will be used to determine the conductivity of the composite Na₂MnFe(CN)₆/K₂MnFe(CN)₆ material.  The electrochemical performance of the cathode material will be analyzed using cyclic voltammetry, and galvanostatic charge/discharge investigation.