Interplay between Phase Transformation Instabilities and Spatiotemporal Reaction Heterogeneities in Particulate Intercalation Electrodes

TL;DR

This paper investigates how phase transformation instabilities and reaction heterogeneities in lithium-ion battery electrodes are interconnected, emphasizing the importance of mesoscale thermodynamics and experimental validation for improved electrode design.

Contribution

It combines theoretical and operando experimental approaches to elucidate the role of thermodynamics and current density in phase transformation behaviors in porous electrodes.

Findings

Reaction heterogeneities are governed by thermodynamics and electrochemical forces.

True local current densities can be much higher than average.

Not all phase separation can be suppressed at high currents in graphite.

Abstract

Lithium-ion batteries rely on particulate porous electrodes to realize high performance, especially the fast-charging capability. To minimize the particle-wise reaction heterogeneities that may lead to local hot spots, deeper understandings of these electrodes at the mesoscale, i.e. hundreds of particles, have become an urgent need. This study reveals that the seemingly random reaction heterogeneities are actually controlled by the interplay between the non-equilibrium material thermodynamics and the external electrochemical driving force. Our operando experiments confirm the true working current density around a single particle that is much higher than the globally averaged current density, can change the behavior of phase transformation. The combined theoretical and experimental analyses reveal that unlike other phase-transforming porous electrodes, not all phase separation processes in graphite can be suppressed at high currents, due to the characteristics of the concentration-dependent exchange current density. The insights highlight the necessity to incorporate materials thermodynamics into electrochemical models to ensure self-consistent understandings of practical porous electrodes toward precision design and management.