Bifunctional composite separator with a solid-state-battery strategy for dendrite-free lithium metal batteries

Lithium (Li) metal anodes have been considered as the “Holy Grail” for next-generation batteries due to their high theoretical capacity and low redox potential. However, nonuniform Li+ deposition leads to hazardous dendrite growth and poor electrochemical performance, which still severely hinders the practical applications of Li metal batteries. Herein, we propose a bifunctional composite separator to guide homogenous Li+ deposition, which smartly learns abundant experience from the dendrite-free design of solid-state batteries. A hierarchical porous composite solid-state electrolyte (CSE) consisting of polyvinylidene fluoride (PVDF) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is coated on one side of polypropylene (PP) separator to fabricate the composite separator. The interactions between PVDF and LLZTO provide a three-dimensional fast Li+ channel along the PVDF, LLZTO, and PVDF/LLZTO interfaces, which can effectively redistribute uneven Li+ flux coming from the insulated PP separator. In addition, the CSE layer can further immobilize the anions, regulating a facile Li+ transport to evenly deposit on the Li anode. The synergetic effects between Li+ redistribution and anion immobilization result in higher Coulombic efficiency and enhanced cycling stability for Li metal batteries. This work presents fresh insights into CSE modified PP separator, which is an effective and simple solid-state-battery strategy for protected Li metal anodes and large-scale production.