Fast lithium ion transport in solid polymer electrolytes from polysulfide-bridged copolymers

Solid polymer electrolytes (SPEs) are being intensively pursued as a means to develop safe, stable and long-life Li-ion batteries. However, the low Li+ conductivity and transference number in SPEs still impede all-solid-state polymer batteries from practical commercialization. Here, lithium polysulfides that cause a shuttle effect problem in Li–S batteries are reduced on a Poly(ethylene oxide) (PEO) chain as an effective way to stimulate Li+ transport. It is shown that the product of the reduction (main –S4Li) dramatically increases Li+ transport while forming a strong interaction with the PEO matrix through intermolecular interactions. In contrast to PEO electrolytes, the –S4Li grafted electrolyte membranes have a lithium transfer number almost 3 times higher, and the LiFePO4|ScPEO|Li cell shows an ultra-long cycle life exceeding 1200 cycles with a capacity decay of 0.024% per cycle at 1 C. The results reveal lithium polysulfides tremendous potential in a solid-state electrolyte system for improving the ion transport and cycling stability.