Physical Orphaning versus Chemical Instability: Is Dendritic Electrodeposition of Li Fatal?

Abstract

The dendritic electrodeposition of lithium, leading to physical orphaning and chemical instability, is considered responsible for the poor reversibility and premature failure of electrochemical cells that utilize Li metal anodes. Herein we critically assess the roles of physical orphaning and chemical instability of electrodeposited Li on electrode reversibility using planar and nonplanar electrode architectures. The nonplanar electrodes allow the morphology of electrodeposited Li to be interrogated in detail and in the absence of complications associated with cell stacking pressure. We find that physical orphaning is a key determinant of the poor reversibility of Li. We report further that fiber-like, dendritic electrodeposition is an intrinsic characteristic of Li, irrespective of the electrolyte solvent chemistry. With guaranteed electronic access to prevent physical loss, we finally show that a Li metal electrode exhibits high levels of reversibility (99.4% CE), even when the metal electrodeposits are in obvious, dendritic morphologies. We take advantage of these findings to create high-loading (7−8 mAh/cm2) Li||LFP full cells with a nearly unity N:P ratio and demonstrate that these cells exhibit good reversibility.