Improving the Li ion flux by a lithiophilic protective layer and morphological investigations of HSAL formation

Summary:

The increasing demand for high-energy battery systems has led to investigations for replacing the graphite anode of Li-ion batteries with Li metal due to its high theoretical capacity and high negative potential. The combination of a Li metal anode and a Li-ion cathode can enable high energy density batteries due to a significantly higher specific capacity.[1], [2] However, poor cycling performance, low Coulombic efficiency (CE) and the uncontrollable dendrite growth during lithium electrodeposition and electrodissolution still remain as main challenges to be overcome ahead Lithium metal batteries (LMBs) practical application.

One approach to overcome the low performance and the safety issues of LMBs is the development of an artificial SEI (aSEI) to generate a homogeneous Li-ion flux, obtain a protective coating layer that prevents parasitic surface reactions and suppresses the formation of high surface area lithium (HSAL, “lithium dendrites”) .[3], [4] In the past, LixM alloy coating layers have shown an improved cycling behavior due to a reduced overpotential and interfacial resistance during lithium electrodeposition. The lithiophilic alloy coating decreases the HSAL formation caused by a high affinity for Li-ion adsorption and a fast lithium diffusion.[5], [6]

Herein we present a new method to generate a LiZn coating on Li metal by using physical vapor deposition (PVD) under vacuum conditions. Zink as a surface coating is known to lower the energy barrier for Li metal nucleation and causing a more uniform nucleation. Therefore, we applied different Zn coating thicknesses on Li metal and investigated their influence on the nucleation behaviour of Li metal as well as the effect on the cycling performance.