Researchers at Argonne National Laboratory have developed a new approach to cobalt-free Li-ion cathodes that avoids some of the problems with other low-cobalt cathode approaches. A paper on their work appears in the Journal of Power Sources.
In his keynote speech at IBA 2019 in San Diego earlier this year, Arumugam Manthiram from the University of Texas noted that:
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. … 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 LiNi1-y-zMnyCozO2 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.
In their paper, the Argonne team says that the most popular strategy followed thus far toward achieving a low-cobalt cathode has been the development of LiNiO2-like, Ni-rich, layered LiMO2 (M = Ni, Mn, Co; NMC) oxides with low Mn and Co contents, e.g., NMC-811.
However, safety, cycle-life, and cost could remain critical barriers to this approach. Instead, the Argonne team suggests modifications to the prototypical cobalt-free, layered oxide, LiNi0.5Mn0.5O2.
Jason R. Croy, Brandon R. Long, Mahalingam Balasubramanian (2019) “A path toward cobalt-free lithium-ion cathodes,” Journal of Power Sources, Volume 440, 227113 doi: 10.1016/j.jpowsour.2019.227113.