Non-Linear Kinetics of The Lithium Metal Anode on Li₆ PS₅ Cl at High Current Density: Dendrite Growth and the Role of...

Interfacial instability, viz., pore formation in the lithium metal anode (LMA) during discharge leading to high impedance, current focusing induced solid-electrolyte (SE) fracture during charging, and formation/behaviour of the solid-electrolyte interphase (SEI), at the anode, is one of the major hurdles in the development of solid-state batteries (SSBs). Also, understanding cell polarization behaviour at high current density is critical to achieving the goal of fast-charging battery and electric vehicle. Herein, via in situ electrochemical scanning electron microscopy (SEM) measurements, performed with freshly deposited lithium microelectrodes on transgranularly fractured fresh Li6PS5Cl (LPSCl), the LiǀLPSCl interface kinetics are investigated beyond the linear regime. Even at relatively small overvoltages of a few mV, the LiǀLPSCl interface shows non-linear kinetics. The interface kinetics possibly involve multiple rate-limiting processes, i.e., ion transport across the SEI and SE|SEI interfaces, as well as charge transfer across the LiǀSEI interface. The total polarization resistance R_P of the microelectrode interface is determined to be ≈ 0.8 Ω cm² . It is further shown that the nanocrystalline lithium microstructure can lead to a stable LiǀSE interface via Coble creep along with uniform stripping. Also, spatially resolved lithium deposition, i.e., at grain surface flaws, grain boundaries, and flaw-free surfaces, indicates exceptionally high mechanical endurance of flaw-free surfaces toward cathodic load (>150 mA cm^-2 ). This highlights the prominent role of surface defects in dendrite growth.