Lithium-ion batteries have become the choice of power source for portable electronics as they offer much higher energy density than other rechargeable systems. They are also in the process of transforming the transportation sector and beginning to penetrate the utility industry for grid storage of electricity produced from renewable sources like solar and wind. The lithium-ion battery industry is now based on layered LiMO₂ cathodes with fractions of M = Mn, Co, and Ni as each of them has its own advantages and disadvantages. For example, Mn offers good chemical stability without oxygen release, while Co suffers from oxygen release on charging LiCoO₂ beyond ~ 50% as the Co³⁺⁴⁺: t_2g band overlaps with the top of the O^2-:2p band. In contrast, Co offers good structural stability without migrating from the transition-metal layer to the lithium layer via the neighboring tetrahedral sites due to the high octahedral-site stabilization energy, while Mn migrates readily to the lithium layer resulting in a layered to spinel-like phase transition due to the low octahedral-site stabilization energy. Also, Mn is abundant, environmentally benign, and less conductive, while Co has limited abundance, is relatively toxic, and becomes metallic on charging. Ni is in between Co and Mn in all these criteria. To make use of the best out of each of these three ions, the industry is now based on LiNi_1-y-zMn_yCo_zO₂ with (1-y-z) < 0.6 and a significant fraction of Co (z > 0.2). There is a significant drive to reduce the fraction of Co or eliminate it altogether and increase the fraction of Ni. However, LiMO₂ cathodes with a high fraction of Ni suffer from a few serious issues: capacity fade, thermal instability, and air-reactivity due to (i) a series of phase transitions causing internal stress, (ii) high surface reactivity with the electrolyte resulting in the formation of thick solid-electrolyte interphase, and (iii) high surface reactivity with ambient air resulting in a significant amount of LiOH and LiHCO₃ on the surface.

This presentation will first focus on a fundamental understanding of the bulk and surface instability of layered LiMO₂ cathodes, employing advanced characterization tools, such as time-of-flight secondary ion mass spectrometry, x-ray photoelectron spectroscopy, and aberration-corrected transmission electron microscopy, to probe both the layered oxide cathode and graphite anode subjected in full lithium-ion cells to extended cycling (up to 1,500 cycles). The presentation will then focus on developing LiMO₂ cathodes with a cobalt content of as low as 6% with appropriate cationic doping and surface stabilization. Finally, it will also present a path forward to develop cobalt-free LiMO₂ cathodes. Based on the strategies, cathodes with capacities of as high as 220 mAh/g with good cycle life and air stability will be presented.