Nanostructure design of amorphous FePO4 facilitated by a virus for 3 V lithium ion battery cathodes

Abstract

Amorphous iron phosphate nanowires with diameters of 10 to 20 nm were synthesized using genetically engineered M13 virus for lithium ion battery cathodes. Hydrolysis of Fe³⁺ ions has been effectively suppressed by forming conjugates with the virus and synthesizing at low temperature, 4 °C. The M13 virus biological template facilitated elaborate nanostructure design and environmentally benign, low temperature synthesis. By implementing heterostructures with silver, we demonstrated experimentally that uniformly distributed Ag nanoparticles throughout the whole structure appeared more advantageous than locally limited network formation by Ag nanowires in enhancing overall electronic conductivity of the entire system, thereby improving battery performances. Electrochemical properties were further improved by dehydration of structural waters. The synergetic use of biological template and synthetic chemistry could enable the synthesis of anhydrous a-FePO₄ without thermal treatment via low-temperature and eco-efficient chemistry. The first discharge capacity at a discharge rate of C/10 and 1C was 165 mA h g⁻¹ (93% of the theoretical value) and 110 mA h g⁻¹, respectively. These electrochemical properties are comparable to the best reported values for a-FePO₄ synthesized at high temperature. In this study, we set the important step for the practical applications of biological approaches in designing and fabricating energy devices, which may be a promising alternative to the traditional processing techniques that consume energy and are costly.