On immersing two lithium metal electrodes in a solution containing lithium salt and applying a voltage, lithium metal will deposit on the electrode connected to the lower voltage. This process is known as electrodeposition. It has been widely observed that under moderate currents, lithium ions do not deposit to a flat surface but rather spontaneously form sharp needle shapes known as dendrites. Dendrite formation is a major barrier for realizing the lithium metal battery, which not only causes capacity loss but also leads to internal short circuit and safety hazard [1].

We report a discovery that the use of a soft piezoelectric film as separator can effectively suppress the formation of lithium dendrite and stabilize the lithium surface during electrodeposition system [2, 3]. When the film is deformed by any local protrusion because of surface instability of the deposited lithium, a local piezoelectric overpotential is generated to suppress lithium deposition on the protrusion. We have established a theory that integrates electrochemistry, piezoelectricity and mechanics. We developed multiphysics computations to simulate dendrite growth in contact with a piezoelectric film. We find that the dendrite-suppression capability is over 6 orders stronger than the limit of mechanical blocking by any separators or solid-state electrolytes. Simulations show that the mechanism ensures deposition to form a flat surface even if the initial substrate surface has significant protrusions, suggesting its robustness and effectiveness against manufacturing defects. We show that the mechanism is so strong that even a weak piezoelectric material is highly effective, opening up a wide range of materials.

REFERENCES

• Liu, G. and Lu, W. A model of concurrent lithium dendrite growth, SEI growth, SEI penetration and regrowth. Electrochem. Soc.(2017) 164: A1826.
• Liu, G., Wang, D., Zhang, J., Kim, A. and Lu, W. Preventing dendrite growth by a soft piezoelectric material. ACS Mater. Lett.(2019) 1: 498-505.
• Gao, T., Rainey, C. and Lu, W. Piezoelectric mechanism and a compliant film to effectively suppress dendrite growth. ACS Appl. Mater. Interfaces. (2020) 12: 51448–51458.