Insights into the Structural and Thermodynamic Instability of Ni-Rich NMC Cathode

Abstract

The Ni-rich LiNi 1-x-y Mn x Co y O 2 (NMC) layered oxides have been promising materials to replace the LiCoO 2 commercial cathode due to their high operation voltages, low cost, and enhanced capacity. However, structural instability is the main drawback of the Ni-rich NMC system, leading to capacity fading, which prevents its commerce application. While numerous efforts have been made to comprehend and overcome this issue, there remains a lack of systematic phase stability analysis which is an essential factor to be addressed. Herein, systematic firstprinciples calculations were performed in this study to reveal the structural, oxidation, and phase stability of Ni-rich NMC during delithiation. This is the first report on competing phases of Ni-rich NMC at various states of charge (SoCs). The compounds with the spinel and rock salt structures formed during delithiation and oxygen evolution takes place at highly delithiation cases, which are likely the origins of capacity fading and crack formation at the surface. This work also outlined the thermodynamic foundation of doping and oxidation state gradient-based core−shell strategies for resolving the instability and enhancing the capacity retention of Ni-rich NMC layered oxides as cathode materials in Li-ion batteries.

Nickel-Doped Titanium Oxide with Layered Rock-Salt Structure for Advanced Li-Storage Materials

“…The valuable effect of Ni doping was to add the bonus of increased charge–discharge capacity to the excellent cycling stability of the layered rock-salt type. This strategy must be valuable not only for TiO 2 -based anode materials but also metal-oxide-based cathode materials with a cation-disordered rock-salt structure, , Ni-rich layered structure, and phosphate olivine structure …”

The future nickel metal supply for lithium-ion batteries

“…The formation of the spinel and rock salt structures and oxygen evolution at high delithiation cases are likely the origins of capacity fading and crack formation at the surface. 91 The theoretical calculations and in situ characterizations need further development and improvement to disclose undiscovered mechanisms, which is expected to provide significant guidance for the design of Ni-rich cathode materials with superior properties.…”