Operando Structural Rearrangement of Self‐Ion‐Implanted Germanium Films Enables High‐Rate Cycling in Lithium‐Ion Batteries

Germanium (Ge) is a strong contender to produce negative electrodes for lithium-ion batteries. However, the drawbacks of Ge are well known: its volume changes dramatically during cycling, leading to low stability and efficiency. One way to mitigate this problem is to make the material porous, allowing it to accommodate the volume change. The porosity can simultaneously facili- tate ion diffusion through the electrode, improving its performance. Ion implantation is an interesting method to produce porous films since it does not involve liquid-phase chemistry or active material removal. Moreover, it can be integrated with deposition techniques employed in the field of semiconductor processing, like plasma-enhanced chamical vapour deposition (PECVD). For these reasons, in this study, Ge negative electrodes for LIBs were produced as filmd by PECVD directly on the current collector + (Molybdenum foil); then, they were made porous through ion implantation with Ge ions. Their performance (rate capability and stability) was tested through electrochemical cycling. These binder-free electrodes showed a remarkably stable specific capacity of 1360 mAh g−1 for more than 400 galvanostatic cycles at a rate of C/4 and could provide a capacity of 490 mAh g−1 and 280 mAh g−1 at 40C and 60C, respectively. Notably, at high rates, the material undergoes structural changes that gradually enhance its high- current performance, demonstrating its suitability for high-power applications.