Chemo-mechanics and Morphological Dynamics of Si Electrodes in All-Solid-State Li-Ion Batteries

Solid-state electrolytes can enable pure Si anodes for high-energy-density battery applications due to improved interfacial stability over their liquid counterparts. Despite this, both systems suffer from large transient electrode volume changes that cause irreversible capacity losses. In all-solid systems, electrochemically induced strain causes stress on a brittle solid electrolyte, causing contact loss and/or cracking. As a result, tracking mechanics and stress evolution is especially important in developing protocols to mitigate these degradation modes. In this work, we utilize operando ultrasound transmission to study the chemomechanical and morphological dynamics of Si electrodes. We show that stress evolution within the bulk is nonlinearly a function of state of charge and depends on metastable Li x Si phases. We demonstrate operando and noninvasive visualization of porosity changes within all-solid-state Si|NMC full cells. We observe significant, irreversible changes in electrode packing density during the first cycle along with morphological dynamics that depend on the direction of current flow.