The impact of pulsed current waveforms on Li dendrite initiation and propagation in solid-state Li batteries

Lithium dendrites are amongst the key challenges hindering Solid-State Li Batteries (SSLB) from reaching their full potential in terms of energy and power density. The formation and growth of these dendrites cause an inevitable failure at charge rates far below the threshold set by industry (>5 mA/cm2) and are supposedly caused by stress accumulation stemming from the deposited lithium itself. Herein, we demonstrate that MHz pulsed currents can be used to increase the current density by a factor of six, reaching values as high as 6.6 mA/cm2 without forming Li dendrites. To understand the origin of this improvement we propose an extension of previous mechanisms by considering the Li activity as a critical factor. The Li activity becomes relevant when Li is geometrically constrained, and the local plating rate exceeds the exchange current density. Over a critical Li activity, the solid-state electrolyte close to the tip of the dendrite fractures and releases the accumulated elastic energy. These events deteriorate the functional and mechanical performance of the SSLB. Since the buildup of a critical Li activity requires a certain time, the application of current pulses at shorter time scales can be used to significantly improve the rate-performance of SSLB, representing a potential step towards the practical realization of electric vehicles and other emerging applications.