Low‐Cost Regulating Lithium Deposition Behaviors by Transition Metal Oxide Coating on Separator

The application of lithium metal anode, despite being of the highest capacity, is hindered by low Coulombic efficiency (CE) and serious lithium dendrites formation. A strategy of transition metal oxides (TMOs) particles coated porous polypropylene (PP) separator is developed to regulate lithium deposition behaviors through in situ forming artificial solid electrolyte interface (SEI) passivating layers. By virtue of quite low solubilities of TMOs in the electrolyte, the concentration of TMOs in the electrolyte can be maintained at a constant and the dissolved TMOs can be reduced to produce Li2O and Mn particles, which not only function as lithium nucleating seeds but are also involved in the formation of the SEI layer. The sustainably existed trace of TMOs ensures the artificial SEI layer can be re‐healed once damaged by the volume expansion of lithium. With the help of one typical TMO of MnO coating on PP, an interesting dendrite‐free dual layer Li deposition is observed, which significantly improves the CE of Li||Cu cells and cycling life of Li||Li cells. Using MnO coated PP, ultra‐thin lithium films are deposited on copper foils with an in situ constructed SEI passivating layer, which exhibits a much improved cycling performance in liquid ether electrolyte and even better performance in gel polymer electrolyte. With the sustained release of transition metal oxides into the electrolyte from composite separators, the in situ formed Li2O/Mn containing a solid electrolyte interface is endowed with the property of self‐healing, with which, dendrite‐free lithium deposition is obtained, improving the cycling life of lithium metal batteries and providing a novel method to prepare ultra‐thin lithium anodes.