Understanding Substrate Mechanics and Chemo‐Mechanical Behavior of Columnar Silicon Films to Enable Deformation Free Anodes for High‐Energy Li‐Ion Batteries

Abstract Columnar silicon (col‐Si) is a great candidate as anode material to achieve volumetric energy density, outperforming state‐of‐the‐art lithium‐ion batteries. The utilization of col‐Si in industrial scale is mainly restricted by poor cyclic life originating from immense volumetric expansion of Si, resulting in mechanical failure of the electrode. Understanding the mechanic and breathing behavior of col‐Si films coupled with copper current collectors (Cu‐CC) is therefore crucial to mitigate the above‐mentioned issues. In this study, structure‐mechanical changes of col‐Si anodes, which are induced by stress evolution upon (de‐)lithiation of Si, are investigated via operando electrochemical dilatometry and in situ thickness monitoring on material and stack level depending on Cu‐CC thickness (10 and 18 µm) and state‐of‐charge/balancing factor (SoC / N/P ratio). Employing moderately thick Cu‐CC (18 µm) prohibits electrode deformation significantly, achieving energy densities of 1101 and 873 Wh L⁻¹ in multilayered‐pouch cells for N/P ratios of 1.1 and 2.0, respectively. The volume uptake that takes place after the first cycle can strongly be reduced from ∆V_{cell stack}: 55% to 25% by adapting N/P: 2.0 instead of 1.1. Even after volumetric growth (lithiated state), energy densities around 700 Wh L⁻¹ are still achievable, confirming the feasibility of the col‐Si approach.