Mixed-valence metal−organic frameworks (MOFs) have exhibited unique potential in fields such as catalysis and gas separation. However, it is still an open challenge to prepare mixedvalence MOFs with isolated Ce(IV, III) arrays due to the easy formation of Ce III under the synthetic conditions for MOFs. Meanwhile, the performance of Li−S batteries is greatly limited by the fatal shuttle effect and the slow transmission rate of Li + caused by the inherent characteristics of sulfur species. Here, we report a mixed-valence cerium MOF, named CSUST-1 (CSUST stands for Changsha University of Science and Technology), with isolated Ce(IV, III) arrays and abundant oxygen vacancies (OVs), synthesized as guided by the facile and elaborate kinetic stability study of , to work as an efficient separator coating for circumventing both issues at the same time. Benefiting from the synergistic function of the Ce(IV, III) arrays (redox couples), the abundant OVs, and the open Ce sites within CSUST-1, the CSUST-1/CNT composite, as a separator coating material in the Li−S battery, can remarkably accelerate the redox kinetics of the polysulfides and the Li + transportation. Consequently, the Li−S cell with the CSUST-1/CNT-coated separator exhibited a high initial specific capacity of 1468 mA h/g at 0.1 C and maintained long-term stability for a capacity of 538 mA h/g after 1200 cycles at 2 C with a decay rate of only 0.037% per cycle. Even at a high sulfur loading of 8 mg/cm 2 , the cell with the CSUST/CNT-coated separator still demonstrated excellent performance with an initial areal capacity of 8.7 mA h/cm 2 at 0.1 C and retained the areal capacity of 6.1 mA h/cm 2 after 60 cycles.

No abstract

This enabled the soluble polysulfides to be effectively immobilized and further electrochemically transformed into Li 2 S via the formation of thiosulfate/polythionate intermediates over the LLTO/SP-coated separator during the discharge of the battery. As a result, the shuttle effect was effectively inhibited, and particularly the passivation of both the cathode and "dead S" over the separator was largely decreased. These properties ensured that the LLTO@Li-S battery displayed a significantly high specific capacity and rate capability as well as good cycling stability. For the LLTO@Li-S battery with a S loading of 2 mg cm −2 , an initial specific capacity of 1491 mAh g −1 at 0.1C and a residual specific capacity of 459 mAh g −1 at 1C after 1200 cycles had been achieved, while for the LLTO@Li-S battery with a S loading of 5 mg cm −2 , an initial specific capacity of 1046 mAh g −1 and a residual specific capacity of more than 800 mAh g −1 at 0.1C after 50 cycles could be delivered.

No abstract

We investigated the chemical structure of actual oxide cathode emission materials using soft x-ray absorption spectroscopy. High-energy resolution spectra of the Ba 3d absorption edges reveal that the Ba content significantly increases on the surface layers of oxide cathodes down to several tens of nanometers in depth, after the cathode activation process. Furthermore, we will demonstrate that the excess Ba on the surface is only slightly driven by thermal energy, but rather it is induced by the voltage difference applied during cathode activation. This result suggests that the rate controlling step of the Ba enrichment on the surface during activation is the electrolytic transport of Ba ion from the bulk powder to the interface. We assume that the Ba enrichment on the surface originates from the depletion of barium in bulk powder by the electrolytic transport.