Towards optimal performance and in-depth understanding of spinel Li$_4$Ti$_5$O$_{12}$ electrodes through phase field modeling

TL;DR

This paper develops a phase field model for Li$_4$Ti$_5$O$_{12}$ electrodes in Li-ion batteries, accurately predicting performance limitations and providing insights for optimizing electrode design.

Contribution

The study introduces a parameter-free thermodynamic phase field model for LTO electrodes, integrating ab-initio and NMR data for enhanced predictive capability.

Findings

Model accurately predicts electrode performance over a wide current range.

Identifies key processes limiting electrode performance.

Provides design directions for improved LTO electrodes.

Abstract

Computational modeling is vital for the fundamental understanding of processes in Li-ion batteries. However, capturing nanoscopic to mesoscopic phase thermodynamics and kinetics in the solid electrode particles embedded in realistic electrode morphologies is challenging. In particular for electrode materials displaying a first order phase transition, such as LiFePO$_4$, graphite and spinel Li$_4$Ti$_5$O$_{12}$ (LTO), predicting the macroscopic electrochemical behavior requires an accurate physical model. Herein, we present a thermodynamic phase field model for Li-ion insertion in LTO which captures the performance limitations presented in literature as a function of all relevant electrode parameters. The phase stability in the model is based on ab-initio DFT calculations and the Li-ion diffusion parameters on nanoscopic NMR measurements of Li-ion mobility, resulting in a parameter free model. The direct comparison with prepared electrodes shows good agreement over three orders of magnitude in the discharge current. Overpotentials associated with the various charge transport processes, as well as the active particle fraction relevant for local hotspots in batteries, are analyzed. It is demonstrated which process limits the electrode performance under a variety of realistic conditions, providing comprehensive understanding of the nanoscopic to microscopic properties. These results provide concrete directions towards the design of optimally performing LTO electrodes.