Lithium Growth Mechanism at High Current Densities

Abstract

Due to the high energy density of lithium metal anode in the secondary battery much effort has been done to investigate lithium deposition. However, only few publications have been done to analyze the Lithium deposition at current densities (cd) of 5 mA/cm² and more, which are relevant for automotive applications. In this work we show time resolved behavior of lithium deposition with cd varied between 0.1-200 mA/cm². The experiments were made in a pseudo-two dimensional optical cell with a symmetric Lithium configuration. Electrolyte was a 1 mol/l solution of LiTFSI in PC:DC (1:1), at room temperature. The distance between anode and cathode was 1mm and active surface 6x10-4 cm². While deposition at low cd led to a dendritic growth of Lithium, with a high current density 10 mA/cm² a homogenous dendritic sheath of lithium was observed. The dendrite growth mechanism was found to be time dependent and changes during the deposition while all external parameters (current, temperature,…) are kept constant. The growth behavior changes from a homogenously distributed dendritic growth at the beginning to the growth of distinct positions only in an advanced state of the deposition. Optical and electrical signals were correlated in real-time during cycling. A strong indication is given for the formation of “death Lithium” for every cd.