A novel epoxy resin-based cathode binder for low cost, long cycling life, and high-energy lithium–sulfur batteries

An epoxy resin PEI–ER formed by in situ cross-linking between an epoxide compound (ER) and polyethylenimine (PEI) is developed as a new cathode binder for lithium–sulfur (Li–S) batteries. Li–S batteries using this new binder showed high initial specific capacity along with remarkable cycling stability. A composite interlayer of PEI–ER and carbon black is also developed to further enhance the cycling stability. A Li–S battery using a combination of the new binder and interlayer achieved a high initial specific capacity of 1174 mA h g−1 and an excellent capacity retention of 80% after 1000 cycles at a cycling rate of 0.5C with 70 wt% sulfur content in the cathode and an areal sulfur loading of 1.9 mg cm−2, which is among the best cycling stabilities reported for Li–S batteries to date. A Li–S battery with a high areal sulfur loading of 5.4 mg cm−2 demonstrated an initial capacity of 780 mA h g−1, which corresponds to a high areal capacity of 4.2 mA h cm−2, and an excellent capacity retention of 72% after 500 cycles.