Concurrent operando neutron imaging and diffraction analysis revealing spatial lithiation phase evolution in an ultra-thick graphite electrode

TL;DR

This study introduces a combined neutron imaging and diffraction method to observe real-time lithium distribution and phase changes within ultra-thick graphite electrodes during battery cycling, revealing spatial heterogeneities and phase evolution.

Contribution

It presents a novel multi-modal operando technique that simultaneously captures macroscopic and crystallographic data on lithium dynamics in thick electrodes, advancing understanding of internal electrode processes.

Findings

Lithium gradients and phase formations vary spatially during cycling.

Delayed lithiation occurs at the electrode center, while SEI forms near the separator.

The method can study lithium diffusion and phase kinetics in thick electrodes.

Abstract

Energy efficient, safe and reliable Li-ion batteries (LIBs) are required for a wide range of applications. Charging capabilities of thick electrodes still holding their stored high-energy is a most desirable characteristic in future advanced LIBs. The introduction of ultra-thick graphite anode meets limitations in internal electrode transport properties, leading to Li-ion gradients with detrimental consequences for battery cell performance and lifetime. Yet, there is a lack of experimental tools capable of providing a complete view of local processes and evolving gradients within such thick electrodes. Here, we introduce a multi-modal operando measurement approach, enabling quantitative spatio-temporal observations of Li concentrations and intercalation phases in ultra-thick, graphite electrodes. Neutron imaging and diffraction concurrently provide correlated information from the macroscopic scale of the cell and electrode down to the crystallographic scale portraying the intercalation and deintercalation processes. In particular, the evolving formation of the solid electrolyte interphase (SEI), observation of gradients in total lithium content, as well as in the formation of ordered LixC6 phases and trapped lithium have been mapped throughout the first charge-discharge cycle of the cell. Different lithiation stages co-exist during charging and discharging of an ultra-thick composite graphite-based electrode; delayed lithiation and delithiation processes are observed at the central region of the electrode, while the SEI formation, potential plating and dead lithium are predominantly found closer to the interface with the separator. The study furthermore emphasizes the potential of the method to study Li ion diffusion and the kinetics of lithiation phase formation in advanced ultra-thick electrodes.