Resisting Dendrites in Lithium Batteries, One Pinhole at a Time

For humanity to successfully transition from fossil fuels, the mismatch in the demand and supply of renewable energy must be addressed by reliable, high energy storage systems. One promising energy storage system is the lithium metal battery (LMB), owing to the high gravimetric capacity of lithium (3860 mAh/g). The potential gain in volumetric and gravimetric energy density offered by LMBs could usurp today’s lithium-ion battery technology and revolutionize energy storage. However, the lifetime of LMBs is hindered by morphological instabilities experienced during the electrodeposition of lithium.<br/><br/>Modifications of the solid electrolyte interphase (SEI) and electrolyte are the most common strategies for improving lithium metal morphology. However, electrolyte and SEI engineering are often tedious, based on trial and error, and insufficient for enhancing lithium electrodeposition. Here, we demonstrate a new, alternative strategy for controlling lithium metal morphology and improving electrochemical performance that is independent of the electrolyte and SEI. By modifying the current collector with atomic layer deposited (ALD) thin films of ZnO, SnO₂, and Al₂O₃, we show that lithium deposits atop, rather than beneath, the thin films, resulting in changes in lithium morphology and battery performance that are strongly dependent on the electrical resistance of the ALD films. The results show that low resistance copper modification films like SnO₂ and ZnO provide numerous sites for lithium nucleation and promote the formation of high surface area (fast electrolyte consuming) lithium deposits, while the highly resistive Al₂O₃-modified copper reduces the available sites for lithium nucleation and promotes the formation of low surface area (slow electrolyte consuming) clusters of lithium deposits.<br/><br/>We propose and demonstrate the first recorded mechanism for the connection between electrical resistance and lithium growth - we propose that, in resistive substrates, lithium metal nucleates atop only pinhole or defect sites, then grows laterally by the radial diffusion of lithium ions from the electrolyte. We prove this mechanism analytically, using diffusion controlled current equations, and experimentally by introducing patterned pinholes into a resistive, pinhole-free substrate. We generalize the concept of resistance-controlled morphology and demonstrate high battery performance in three distinct classes of electrolytes, culminating in anode-free pouch cells that retain 60% of their initial discharge capacity after 100 cycles. This work presents a new approach for understanding the electrodeposition of lithium and tuning the performance of lithium metal batteries.