Morphological evolution of a single crystal silicon battery electrode during lithiation and delithiation: An operando phase-contrast imaging study

Operando phase-contrast radiography combined with impedance spectroscopy and electron microscopy is applied to study the morphological changes in a lithium-silicon cell over several cycles. The single-crystal silicon (100) surface is employed as a working electrode. A checkerboard-like cracking pattern aligned with the crystallo-graphic axis is formed in the 4th cycle during the second step of the delithiation. With the crack position kept fixed, this crack pattern vanishes during lithiation and gets more pronounced in the subsequent cycles. This pattern forms just after the first delithiation peak that corresponds to the decomposition of the highly lithiated phase. It vanishes during lithiation in the potentiostatic step. Therefore, capacity-limited cycling, which partly maintains the highly lithiated phase, may avoid the formation of fractures. The surface area of the crack cells remains almost constant with increasing cycle numbers, and no electrochemically inactive sites were observed.