Dendritic cracking in solid electrolytes driven by lithium insertion

During charging of a battery with a lithium metal electrode and a solid electrolyte, a crack in the electrolyte adjacent to the metal electrode will be infiltrated by lithium, forming a dendrite. As further lithium is inserted into the crack, pressure in it will build up. The pressure in the lithium in the crack rises very rapidly during normal rates of charging, reaching 1 GPa within seconds. Such high pressure may cause the crack to propagate; crack extension will relax the pressure in the crack, but high pressure will be restored quickly in the longer crack, which will again propagate. This process continues until the crack touches the counter electrode, causing a short-circuit. Alternatively, the high pressure in the crack can block the redox reaction that injects lithium into it, making the crack non-propagating. We find that this situation occurs for cracks shorter than a critical length. Therefore, to avoid short-circuits of this type it is a requirement that the pressure be sufficient to block the redox reaction before dendrite extension takes place. This places restrictions on allowable lengths for pre-existing cracks and on permissible charging rates. We also find that dendrite cracks can grow subcritically due to cyclic fatigue.