Void growth within Li electrodes in solid electrolyte cells

The growth of voids at the electrode/electrolyte interface of a solid state Li battery is analysed by establishing a framework that uses the Onsager formalism to couple the power-law creep deformation of the Li electrode and flux of Li + through a single-ion conductor solid electrolyte. For realistic combinations of the interfacial resistance and electrolyte conductivity, standard Butler-Volmer kinetics for the interfacial flux does not provide sufficient flux focussing to initiate void growth and so a modified kinetics is adopted where the interfacial resistance is decreased by the presence of dislocations within the creeping Li electrode. Micron-sized pre-existing voids shrink under stripping conditions as flux focussing on the periphery of these voids is always low. However, spatially inhomogeneous creep in the electrode around a hemispherical impurity particle reduces the interfacial resistance with consequent significant flux focussing at the periphery of the impurity. This flux focussing results in void growth with two distinct regimes of behaviour: (i) at low currents stable but small voids form while (ii) at higher currents large voids form but these ultimately collapse. No conditions are identified for which isolated voids are predicted to grow larger than 10 mu m in size suggesting that cell failure does not occur by the growth of isolated voids. We therefore propose a hypothesis for the coalescence of voids that initiate around impurity particles being deposited on the interface during stripping of the electrode. The ensuing predictions are consistent with measurements of cell failure and provide clues of the failure mechanisms due to void growth. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. T

Automated summary

The growth of voids at the electrode/electrolyte interface in solid-state Li batteries is analyzed using a framework that incorporates power-law creep deformation of the Li electrode and Li+ flux through a single-ion conductor solid electrolyte. The results suggest that void growth is influenced by the interfacial resistance, electrolyte conductivity, and the presence of dislocations within the electrode. The findings provide insights into the failure mechanisms of Li batteries due to void growth.