Fabrication of Borate-Based Porous Polymer Electrolytes Containing Cyclic Carbonate for High-Performance Lithium Metal Batteries

Abstract

A series of borate-based porous polymer electrolytes (B-PPEs) is prepared by incorporating the copolymers containing cyclic boroxine and cyclic carbonate groups into poly(vinylidene fluoride) (PVDF) through the phase inversion method. The dense and well-interconnected pores are obtained in the polymer matrix when the content of the copolymer reached 40 wt %. The ethylene–oxygen chain segments in the copolymer can facilitate the mobility of polymer chains and form the uniform distribution of pores in the B-PPEs. The B-PPEs show an enhanced ionic conductivity of 1.32 × 10–3 S cm–1 at 30 °C, which is due to the uniform well-interconnected pores in the polymer host. The cyclic carbonate units interact with the liquid electrolyte, which could improve the electrolyte uptake capacity of the polymer matrix. Benefited from the Lewis acid–base interactions between boron moieties and the anions of the lithium salt, the lithium-ion transference number of B-PPEs is also significantly improved. Compared to the pure PVDF-based electrolyte, the Li/B-PPEs/Li cell displays a very stable polarization voltage and the long-time cycling for 1000 h at a current density of 0.2 mA cm–2. Moreover, the Li/B-PPEs/LiFePO4 cells deliver a higher capacity of 143.0 mAh g–1 at 0.2 C and 86% capacity retention after 150 cycles. The B-PPEs could be a promising candidate for enhancing the safety and electrochemical properties of lithium metal batteries.