Self-extinguishing Janus separator with high safety for flexible lithium-sulfur batteries

Abstract

Flexible lithium-sulfur (Li-S) batteries are considered one of the most promising candidates for high-energy-density storage devices in wearable electronics. However, the safety problem severely restricts the practical application of Li-S batteries because of the possible occurrence of thermal runaway caused by battery short circuits and combustible components, particularly under bending conditions. The development of advanced separators that can suppress lithium dendrite growth and are incombustible is the key to improving the safety of flexible Li-S batteries. In this work, a nonflammable multifunctional Janus separator with self-extinguishing capability, high thermal stability, high thermal conductivity, good electrolyte infiltration, uniform lithium deposition, and efficient polysulfide shuttling inhibition, is proposed. The separator is composed of polyacrylonitrile (PAN) fiber and decabromodiphenyl ethane (DBDPE) membrane as well as functional layers of boron nitride (BN) for suppressing lithium dendrite growth and reduced graphene oxide (rGO) for accelerating the sulfur convention kinetics. As a result, the Li-S battery with a sulfur mass loading of 2.7 mg cm−2 delivers a specific capacity of 916.8 mA h g−1 after 100 cycles at 0.1 C and maintains a stable performance during intermittent thermal shock. Moreover, the Li-S pouch cell with a sulfur mass loading of 8 mg exhibits a high capacity of 6.3 mA h under bending conditions.