Improved Capacity Retention of Metal Oxide Anodes in Li-Ion Batteries: Increasing Intraparticle Electronic Conductivity through Na Inclusion in Mn<inf>3</inf>O<inf>4</inf>

In this work, we significantly improve the cyclability of Mn3O4 anodes in Li-ion batteries by enhancing its intraparticle electronic conductivity by doping with Na. Na was selected because, unlike typical transition-metal dopants, it is non-surface redox active in the potential window where the metal oxide conversion reaction occurs, and hence is more electrochemically stable during charge/discharge cycling. This work presents the first time that Na has been used as a dopant in metal oxide anodes, and the result is excellent capacity retention and rate capability. More specifically, Na was added to Mn3O4 (to achieve a Mn/Na ratio of ca. 9 : 1), impregnated onto a carbon nanotube matrix. The concentration of Na considering the entire composition of the anode material was 0.5 at %. These electrodes were able to achieve a capacity of approximately 750 mAh/g at a 1C rate, and retain over 99 % of that capacity over 500 cycles. They were also able to provide nearly twice the theoretical capacity of conventional graphite anodes under high rate discharge (609 mAh/g @ 5C), as well as achieve a higher capacity at 10C (ca. 350 mAh/g) than conventional graphite electrodes can at 1C.