Sulfur double locked by a macro-structural cathode and a solid polymer electrolyte for lithium-sulfur batteries

Both macro-structural cathode materials and a metal-organic framework (MIL-53(Al)) modified solid polymer electrolyte are used to inhibit polysulfide dissolution and shuttling in all-solid-state lithium-sulfur batteries. At 80 degrees C, the discharge capacities of 1520 mA h g(-1) in the first cycle at 0.2 C and 325 mA h g(-1) in the 1000th cycle at 4 C are obtained, demonstrating exceptional high rate capability and long-term cycling performance of the batteries. Mechanisms for such an enhancement are investigated by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and thermo-gravimetric analysis techniques. In the EIS spectra there is no semicircle caused by the polysulfide shuttling and reaction at the electrolyte/Li interface, proving that polysulfide dissolution is adequately inhibited. The XPS spectra on the Li anode surface after 10 discharge/charge cycles show that sulfur and polysulfide do not transfer from the cathode to the anode. The -C-S-bond in the original cathode is observed by XPS, indicating that sulfur is linked to macro-structural cathode materials by the thermal treatment. In addition, an intermediate forms during cycling and displays steady electrochemical reversibility. These data indicate that the macro-structural cathode and solid polymer electrolyte play crucial roles in blocking polysulfide dissolution and shuttling, and lead to the outstanding cycling performance of all-solid-state lithium-sulfur batteries.