Homogeneous and Stable Lithium Electrodeposition through a Thin Single-Ion Conducting Layer for High Cycling Stability of Lithium Metal Secondary Batteries

The inhomogneous and unstable Li electrodeposition of lithium metal electrode has been a major impedment to the realization of rechargeable lithium metal batteries. Although polymeric single ion conductors can provide more homogeneous Li electrodeposition owing to their high Li ion transference number, their poor ionic conductivities prevent practical battery design. In the paper, we sugest a hybrid electrolyte based on a few micron-thick single-ion conducting layer laminated on Li metal electrode and a liquid electrolyte, which allows rapid Li⁺ transport and stable Li electrodeposition. The introduction of the single-ion conducting layer increases Li⁺ transference number from 0.451 to 0.855, consequently suppressig the generation of Li dendrite as demonstrated by SEM and impedance analysis. Reducing the thickness of the single-ion conducting layer down to a few microns and incorporating the bi-ionic liquid electrolyte permit room-temperature operation at high current densities.  The Li/Li symmetric cell with the hybrid approach operate at a high current density of 10 mA cm^-2 for more than 2000 h, which corresponds to more than five-fold enhancement compared to bare Li metal electrode, and the protyopye Li/LiCoO₂ battery offers cycling stability more than 350 cycles at 0.2 C, demonstraing the practical applicability of this approach.