Revealing evolving affinity between Coulombic reversibility and hysteretic Li-Si phase transformations

TL;DR

This study uncovers how cyclic amorphous-crystalline phase transformations in nano-structured silicon anodes influence Coulombic efficiency, revealing that iterative phase changes can optimize battery performance over many cycles.

Contribution

It demonstrates that hysteretic Li-Si phase transformations, rather than simple volume changes, govern Coulombic efficiency evolution, providing new insights into silicon anode degradation and optimization.

Findings

Iterative amorphous-crystalline phase transformations improve CE profiles.

Phase transformation cycles significantly alter electrochemical properties.

CE evolution is linked to structural changes observed via atomistic methods.

Abstract

Nano-structured silicon anodes are attractive alternatives to graphite in Li-ion batteries. Despite recent remarkable progresses in numerous Si-C composites, the commercialisation with significance is still limited. One of the most critical issues remained to understand is fundamentals on Li-Si Coulombic efficiency, namely, CE. Particularly, it is key to quantitatively and qualitatively resolve CE alterations and evolutions by the various Li-Si structural changes over longer cycling. However, such work is surprisingly scarce. Here, we provide new findings that iterating the hysteretic amorphous-crystalline Li-Si phase transformations accumulatively governs CE evolutions, the manner of which is numerically distinguished from incremental amorphous Li-Si volume changes. The iterations, usually featured as capacity degradation factors, can form the most efficient CE profiles over hundreds of cycles, i.e. minimising accumulative irreversible Li consumption, among the given Li-Si reaction sequences. Combined with atomistic probing methodologies, we show that the iteration drastically alters electrochemical and structural characteristics, which is synchronised with the CE behaviours.