Fictitious phase separation in Li layered oxides driven by electro-autocatalysis
Journal
Nature Materials
Journal Volume
20
Journal Issue
7
Pages
991-999
Date Issued
2021
Author(s)
Chen C.-C
Abstract
Layered oxides widely used as lithium-ion battery electrodes are designed to be cycled under conditions that avoid phase transitions. Although the desired single-phase composition ranges are well established near equilibrium, operando diffraction studies on many-particle porous electrodes have suggested phase separation during delithiation. Notably, the separation is not always observed, and never during lithiation. These anomalies have been attributed to irreversible processes during the first delithiation or reversible concentration-dependent diffusion. However, these explanations are not consistent with all experimental observations such as rate and path dependencies and particle-by-particle lithium concentration changes. Here, we show that the apparent phase separation is a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions, that is, an interfacial exchange current that increases with the extent of delithiation. We experimentally validate this population-dynamics model using the single-phase material Lix(Ni1/3Mn1/3Co1/3)O2 (0.5 < x < 1) and demonstrate generality with other transition-metal compositions. Operando diffraction and nanoscale oxidation-state mapping unambiguously prove that this fictitious phase separation is a repeatable non-equilibrium effect. We quantitatively confirm the theory with multiple-datastream-driven model extraction. More generally, our study experimentally demonstrates the control of ensemble stability by electro-autocatalysis, highlighting the importance of population dynamics in battery electrodes (even non-phase-separating ones). ? 2021, The Author(s), under exclusive licence to Springer Nature Limited part of Springer Nature.
Subjects
Diffraction
Electrodes
Lithium compounds
Lithium-ion batteries
Population dynamics
Statistical mechanics
Transition metals
Concentration-dependent diffusion
Electrochemical reactions
Interfacial exchanges
Many-particle systems
Non-equilibrium effects
Population dynamics models
Single-phase composition
Single-phase materials
Phase separation
SDGs
Type
journal article