Synergistic Effects of Surface Coating and Bulk Doping in Ni‐Rich Lithium Nickel Cobalt Manganese Oxide Cathode Materials for High‐Energy Lithium Ion Batteries

Abstract

Ni‐rich layered oxide cathodes are promising candidates to satisfy the increasing energy demand of lithium‐ion batteries for automotive applications. Thermal and cycling stability issues originating from increasing Ni contents are addressed by mitigation strategies such as elemental bulk substitution (“doping”) and surface coating. Although both approaches separately benefit the cycling stability, there are only few reports investigating the combination of two of such approaches. Herein, the combination of Zr as common dopant in commercial materials with effective Li2WO4 and WO3 coatings was investigated with special focus on the impact of different material processing conditions on structural parameters and electrochemical performance in nickel‐cobalt‐manganese (NCM) || graphite cells. Results indicated that the Zr4+ dopant diffusing to the surface during annealing improved the electrochemical performance compared to samples without additional coatings. This work emphasizes the importance to not only investigate the effect of individual dopants or coatings but also the influences between both.

The Effect of Doping Process Route on LiNiO2 Cathode Material Properties

“…56,60 Vice versa, Zr 4+ as a dopant is prone to enrich and phase separate at the surface of CAM particles, forming an additional Li 2 ZrO 3 phase. 31,51,53,61,62 With this limited bulk solubility in mind, only some studies focused on industrially relevant dopant concentrations, i.e. below 1 mol%.…”

“…below 1 mol%. 24,25,47,61,62 The atom position of Zr 4+ in the structure is not fully understood, with literature reporting localization either in the lithium 63 or transition-metal layer, 23,43 or possibly both. 39,53,64 Main effects and advantages attributed to the dopant include increased c lattice parameter, faster lithium diffusion, smoother H2/ H3 phase transition, less volume change during delithiation, less crack formation and reduced surface-layer formation, ultimately resulting in longer cycle life, improved rate capability, reduced impedance and less polarization of the CAM.…”

A review of the degradation mechanisms of NCM cathodes and corresponding mitigation strategies

“…Similar to wet-chemical coating procedures, NCM doping most often involves a calcination step at the end of material synthesis, which, analogously to the calcination step during coating, can cause migration of the introduced elements to the surface to form a coating. As has been shown for Zr 4+ dopant, temperatures as low as 400°C cause migration of Zr 4+ to the surface of the particles to form a Zr-containing coating [253]. Similarly, doping NCM with Sb was shown to also create an Sb oxides coating when annealing in O2 atmosphere at 750 °C [254].…”

Armor‐like Inorganic‐rich Cathode Electrolyte Interphase Enabled by the Pentafluorophenylboronic Acid Additive for High‐voltage Li||NCM622 Batteries

“…The common strategies for improving the stability of high‐voltage cathodes are doping, constructing artificial cathode electrolyte interphase, and electrolyte engineering [15–19] . Among them, electrolyte engineering is more effective and economical by inducing cost‐effective solvents or additives into conventional carbonate electrolytes [20–22] .…”