Tailoring Mechanical Properties of Germanium Anodes via Metal Incorporation for Improved Cycle Stability

TL;DR

This study introduces a metal doping strategy, especially with Yb, to enhance the cycle stability of germanium anodes in lithium-ion batteries by mechanically softening the material and reducing damage.

Contribution

It demonstrates that trace metal doping, notably with Yb, significantly improves Ge anode longevity by mechanical softening, shifting design focus to electrode compliance.

Findings

Yb doping extends Ge anode lifetime by about three times.

Metal size correlates negatively with anode hardness, promoting mechanical softening.

Yb doping reduces high-rate performance but enhances durability.

Abstract

Achieving long-term stability in high-capacity lithium-ion battery anodes remains a critical challenge. In this study, we present a materials-intrinsic strategy for extending the cycle life of Ge, a promising next-generation anode material, through trace doping with metal elements. We systematically investigated the effects of small additions of various metals and found that elements with large atomic size, particularly Yb, markedly improved the cycling stability without sacrificing the initial capacity, while appropriate Yb doping enhanced the anode lifetime by approximately a factor of three. Structural and electrochemical analyses revealed that this improvement originates from mechanical softening of the Ge anode, which suppresses lithiation-induced damage such as cracking and delamination. Nanoindentation measurements further showed a strong negative correlation between dopant atomic size and film hardness, establishing anode softening as a new design principle for damage-tolerant electrodes. Although Yb doping reduced the rate capability at high C-rates, the present results demonstrate a clear shift in design strategy from volume-change suppression to mechanical compliance. These findings provide a useful framework for stabilizing high-capacity alloy anodes through atomic-scale mechanical control.