3D ink-printed, sintered porous silicon scaffolds for battery applications
The fabrication of 3D ink-printed and sintered porous Si scaffolds as electrode material for lithium-ion batteries is explored. A hierarchically-porous architecture consisting of channels (~220 μm in diameter) between microporous Si struts is created to accommodate the large volume change from Si (de)lithiation during electrochemical (dis)charging. The influence of sintering parameters on Si strut porosity and the resulting mechanical and electrochemical properties of the scaffolds are studied experimentally and computationally. Varying sintering temperatures (1150–1300 °C) and sintering times (1–16 h) the open porosity within the Si filaments can be tailored between 46 and 60%. Pore size (3–6 μm) and wall thickness (3–8 μm) can be adjusted to tailor the surface-to-volume ratio. Computational results show that maximum capacity is expected at ~50% Si strut porosity, balancing short diffusion lengths and sufficient volume of active material. Stress concentrations are reduced at higher filament porosities albeit at the cost of energy density. For a filament porosity of 46%, hierarchically porous Si microlattice electrodes display gravimetric and volumetric capacities as high as 2,990 mA h g−1 and 2,860 mA h cm−3, respectively. The simple 3D printing + sintering approach provides further opportunities for optimization of Si electrodes by geometrical freedom.