Mass-Scalable Molecular Monolayer for Ni-Rich Cathode Powder: Solution for Microcrack Failure in Lithium-Ion Batteries.

Abstract

Ni-rich layered oxide with high reversible capacity, low manufacturing cost, and high potential is recognized as the best practical cathode material for high energy density lithium-ion batteries for affordable electric vehicles. However, they suffer from a poor cycle life owing to internal microcracks, which have been perceived to be due to anisotropic volume changes. Herein, the failure mechanism as well as improved cycle life is demonstrated by a self-assembled molecular monolayer (SAM) on Ni-rich layered oxide powder with a gas-phase precursor of octyltrichlorosilane (OTS), enabling mass-scalable manufacturing. The SAM process with a low heating temperature of 130 °C compared to the commonly used coating is also suitable to the chemically fragile Ni-rich layered oxide. Also, a homogeneous angstrom-level OTS coating is beneficial for preserving the energy density of batteries. In particular, OTS, with electrolyte-phobic functionality, is very effective for mitigating the inherent microcrack failure of the particles by reducing the internal electrolyte decomposition by controlling electrolyte wetting into secondary particles. Systematic surface analyses of the cross section of Ni-rich electrode with the OTS coating found greatly improved particle stability after 100 cycles in comparison with pristine material.