Understanding boron chemistry as the surface modification and electrolyte additive for Co-free lithium-rich layered oxide

Lithium-rich layered oxide (LRLO) stands out as a highly promising cathode material for the next generation of Li-ion batteries, owing to its exceptional lithium storage capacity. The absence of cobalt in LRLO's composition provides an additional advantage, enabling cost-effective production and thereby improving the feasibility of large-scale manufacturing. Despite these promising attributes, LRLO has encountered challenges related to poor cycling performance and severe voltage decay, impeding its practical application. In addressing these challenges, a surface modification technique involving lithium borate (LBO) is employed through a dry coating method. The LBO-coated LRLO exhibits a uniform surface layer with a thickness of 15 nm. Furthermore, the performance of LBO-coated LRLO in a full cell is synergistically enhanced when combined with lithium bis(oxalato)borate (LiBOB) as an electrolyte additive. A discharge capacity retention of 82% is achieved after 400 cycles at room temperature. These substantial improvements are attributed to the continual reaction between boron species on the LRLO cathode surface and PF${}_6$${}^{-}$ anions in the electrolyte. This reaction generates BF${}_4$${}^{-}$ and suppresses HF acid formation during the high voltage charging process, demonstrating LRLO's potential for practical implementation. (© 2024 The Author(s). Advanced Energy Materials published by Wiley‐VCH GmbH)