Deconvoluting Effects of Lithium Morphology and SEI Stability at Moderate Current Density Using Interface Engineering

Abstract Lithium (Li)‐morphology and solid electrolyte interphase (SEI) are among the most significant performance regulators in Li‐metal batteries (LMBs). While both Li‐morphology and SEI composition play key roles in the cyclability of LMBs, less is understood about the individual contributions of each factor to overall Li reversibility, particularly at a practical current density (1 mA cm −2 ) at which the kinetics of both factors are not naturally separated. Herein, an interface engineering approach is introduced to deconvolute the impacts of Li‐morphology and SEI composition on battery performance. By using interfacial nanofilms with differing resistivity (resistive HfO 2 versus conductive ZnO), the morphology of Li is varied, and by virtue of similar acidic character of the nanofilms, the formation of anion‐rich SEIs is maintained. It is established that although the surface acidity of the thin films enables preformation of a more anion‐rich SEI, it is not preserved after Li plating. It is further shown that resistance‐controlled, low‐surface‐area Li‐morphology exhibits up to threefold increase in stable cycle life when tested in multiple electrolytes. Overall, these findings explain why Li‐morphological control is more advantageous for performance improvement than preformed SEI modulation due to the inherent challenges in SEI preservation.