Fire-retardant sp3 boron-based single ion conducting polymer electrolyte for safe, high efficiency and dendrite-free Li-metal batteries

Abstract

Single lithium ion conducting polymer electrolytes (SIPEs) are an emerging class of alternative polymer electrolytes for protecting lithium metal anode. This work explores a fully aromatic sp3 boron based SIPE, lithium poly (4,4′-dihydroxydiphenyl sulfone borate), Li-PSB, via a one-step synthetic procedure. A series of highly porous SIPE membranes, defined as po-PBSBs, comprising of Li-PSB and a fully aromatic polybenzimidazole (PBI) binder are firstly prepared. As a polymer electrolyte, po-PBSB exhibits high lithium ion transference number of close to unity, high ionic conductivity, excellent thermal dimensional stability and promising flame-retardant. X-ray Photoelectron Spectroscopy (XPS) and Density Functional Theory (DFT) calculations depict multi-coordinated lithium ion transport channels in the po-PBSB membranes. By serving as polymer electrolyte in lithium metal batteries (LMBs), Li/LiFePO4 (LFP) cell, the po-PBSB shows an effective suppression of lithium dendrite growth. As a consequence, po-PBSB based Li/LFP cell demonstrates superior cycling performance remaining 76.1% of its initial capacity with nearly 100% coulombic efficiency at 1.0C after 200 cycles. The excellent performance may be ascribed to the remarkable lithium ion transference number, high organic solvent absorption in pores and thermal and electrochemical stabilities of the po-PBSB. We believe that the novel SIPE materials have great potential for application in high-safety LMBs.