Ultra-high power capabilities in amorphous FePO4 thin films

• Rapid Li+ pseudocapacitance observed for the first time in an amorphous material.
• Amorphous FePO4 thin film electrodes behave as pseudocapacitors.
• Specific power of 1 MW kg−1 obtained in addition to excellent cycling performance.
• Self-enhancing kinetics resulted in 50% increased specific capacity during cycling.

Record breaking electrochemical properties of FePO4 have been found through investigation of the thickness dependent electrochemical properties of amorphous thin film electrodes. Atomic layer deposition was used for production of thin films of amorphous FePO4 with highly accurate thickness and topography. Electrochemical characterization of these thin film electrodes revealed that the thinner electrodes behave in a pseudocapacitive manner even at high rates of Li+ de/intercalation, which enabled specific powers above 1 MW kg−1 FePO4 to be obtained with minimal capacity loss. In addition, a self-enhancing kinetic effect was observed during cycling enabling more than 10,000 cycles at current rates approaching that of a supercapacitor (11s charge/discharge). The current findings may open for construction of ultra-high power battery electrodes that combines the energy density of batteries with the power capabilities of supercapacitors.

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