Uniform Lithium Deposition Achieved by SnO2/Hydroxypropyl Methyl Cellulose Composite Separator toward Ultrastable Lithium Metal Batteries

The uncontrollable growth of lithium (Li) dendrites impedes the development of practical applications for the long-awaited lithium metal batteries. In this work, a strategy is proposed to protect the Li anode with a composite separator of in situ formed SnO2 and hydroxypropyl methyl cellulose (HPMC) on the polyethylene (PE) substrate. Based on the use of SnO2/HPMC@PE separator, the Li||Li cell has an ultralong cycle life of more than 2000 h and ultralow-voltage hysteresis of 11.1 mV, whereas the cell with PE separator only has the cycle life of 800 h and the voltage hysteresis of up to 222.9 mV. Moreover, Li||LiNi0.6Co0.2Mn0.2O2 (NCM622) has an initial discharge capacity of 142.3 mAh g–1 and a capacity retention of 77.9% after 250 cycles at 1 C, which are higher than those of PE (140.6 mAh g–1 with retention of 59.5%). All of the enhanced performance can be ascribed to a regulable SEI film that can be formed on the Li foil in direct contact with the SnO2 layer, which decreases the Li nucleation overpotential and facilitates ultimately uniform Li deposition. This work demonstrates the feasibility of using a modified separator to achieve stable Li metal batteries.