Highly pressure-resistant and high-rate ultrathick micro-Si anodes for 3D microbatteries via direct-ink-writing of directionally continuous porous microstructure

3D microbatteries, featuring customizable and thick electrode designs, are crucial for miniaturized and specialized electronic devices. However, the practical implementation of thick 3D microelectrodes is often challenged by sluggish ion transport and mechanical instability under external and internal stresses. Here, we developed pressure-resistant ultrathick micro-Si 3D microelectrodes using an in-situ directional freezing-assisted direct-ink-writing 3D printing approach. This approach enables the construction of ultrathick electrodes up to 2.7 mm, achieving an ultrahigh areal capacity of 14.0 mAh cm^-2. The 3D-printed thick electrodes demonstrate remarkable pressure-resistant capability due to the formation of directionally continuous porous microstructure, providing a high compression modulus of ∼3.04 MPa. The directional pore microstructure not only effectively resists external stress and mitigates micro-Si volumetric changes but also significantly enhances ion diffusion, resulting in improved rate capability and cycle stability compared to the non-directional one. This study presents a reliable method for fabricating pressure-resistant ultrathick 3D microelectrodes with high mechanical and electrochemical performances, paving the way for customized 3D microbattery applications.