Stacking pressure homogenizes the electrochemical lithiation reaction of silicon anode in solid-state batteries

Several tens of MPa stacking pressure is usually necessary to fully utilize the capacity of energy-dense silicon anode in solid-state batteries, presenting significant hurdles for real applications. It is thus critical to establish the link between the macroscopic stacking pressure and the microscopic electrochemical processes. In this work, we used titration gas chromatography to quantify the capacity-loss processes of silicon anodes under different stacking pressures. Furthermore, time-of-flight secondary ion mass spectrometry, electron microscopy, and phase-field modeling techniques were used to map the spatial distribution of chemical species (e.g., LixSi alloys), stress, and electrochemical overpotential upon (de)lithiation processes of the silicon anode. High stacking pressure was observed to significantly increase the extent that a Si anode can be lithiated because of the increased reaction homogeneity resulting from the strong electro-mechanical coupling, while its impact over lithium loss during the first cycle is rather limited. Our work provides a basis to unlock the full potential of Si-anode based solid-state batteries at near-ambient stacking pressure and calls for innovative strategies to minimize or compensate for the lithium loss at the first cycle.