Chemical Speed Dating: The Impact of 52 Dopants in Na–Mn–O Cathodes

Abstract

Na–Mn–O cathodes are very promising for sodium-ion batteries but suffer major setbacks related to long-term cycling and stability in air. With our high-throughput approach, a systematic investigation of 52 different dopants of Na0.66MnO2 from across the periodic table was performed. The chemical composition of Na0.66Mn0.9M0.1O2+δ (M = dopant) is utilized to unravel the impact of dopants on the layered structure and investigate how different dopants influence the battery performance and air and moisture stability. A broad range of doping was possible, with 20 different dopants fully integrating into the Na–Mn–O structures, including several previously unstudied dopants (Si, Sc, Ga, Rb, Rh, Cs, Re, and Tl). This yields high-interest novel cathodes, including a Rb-doped sample with a high specific capacity of 200 mA h g–1, as well as Mo- and Nb-doped samples with excellent capacity retentions of 98% and 100%, respectively, after 10 cycles compared to 92% in undoped Na0.66MnO2. The air and moisture stability of the cathode material is studied systematically, and a number of compositions show ultrahigh stability in air. This systematic approach provides a rapid overview of the benefits of individual dopants and also provides an excellent opportunity to elucidate trends across the periodic table. Significantly, we find that the presence of reversible anionic redox (absent in the undoped samples) correlates remarkably well to the bond valence sum of the dopants, implying that dopants can be used to tune the polarity of M–O bonds and encourage anionic redox behavior. Such “speed dating” reveals fundamental chemical insights and guides further design.