PEO-coated sulfur-carbon composite for high-performance lithium-sulfur batteries

Poly(ethylene oxide)-coated sulfur/carbon (S/C/PEO) composite with a high sulfur loading is prepared to improve the performance of lithium-sulfur batteries. By magnetic string, 3.7 wt% PEO is coated onto the surface of ball-milling obtained S/C composite, leading to synthesis of S/C/PEO composite containing 78 wt% S. It is confirmed from a series of measurements that PEO covers the S/C composite uniformly, and PEO coating is quite effective in stabilizing the electrochemical performance. When employed as cathode for lithium-sulfur batteries, S/C/PEO delivers an initial discharge capacity of 989.6 mAh g−1 and remains 648.3 mAh g−1 after 110 cycles at a discharge/charge rate of 1 C (based on sulfur weight). Meanwhile, the coulomb efficiency of S/C/PEO composite reaches to ~98 % during the latter 105 cycles. The improved electrochemical performance can be attributed to the formation of PEO coating layer which can keep a tight contact between carbon and sulfur and lead to improved conductivity. Moreover, the PEO coating can act as a flexible cushion to accommodate volume changes of sulfur cathode as well as a barrier to trap soluble polysulfide intermediates during the charge-discharge processes.