Electrochemically Induced Shape-Memory Behavior of Si Nanopillar-Patterned Electrode for Li Ion Batteries

A nanopillar-patterned Si substrate was fabricated by photolithography, and its potential as an anode material for Li ion secondary batteries was investigated. The Si nanopillar electrode showed a capacity of ∼3000 mAh g^-1 during 100 charging/discharging cycles, with 98.3% capacity retention, and it was revealed that the nanopillars underwent delithiation via a process similar to shape-memory behavior. Despite the tensile stress and structural fractures resulting from repeated lithiation, the nanoscale size and residual crystalline tip of the pillar (influenced by the bulk crystalline Si base) enabled recrystallization and transformation into a single-crystalline phase. To the best of our knowledge, this observation of shape memory recrystallization mechanism observation was not reported before for Si used as the active material in Li ion battery applications; these findings are expected to provide new insights into electrode materials for rechargeable batteries.