Al-based metal organic framework derived self-assembled carbon nanosheets as innovative anodes for Li- and Na-ion batteries.

Functional modification and structural design of carbon electrode materials are considered as a cost-effective method to improve their electrochemical performance. In this study, a solvothermal method is applied to realize self-assembly of the metal-organic framework. After simple carbonization and acid treatment, carbon nanosheets with 2D adjustable defective sub-units are successfully prepared for the first time. It is found that carbonization temperature has a significant effect on the carbon skeleton structure. The optimal nanostructures with large specific surface area and appropriate pore size distribution make self-assembled carbon nanosheets having excellent Li/Na-ion storage properties. In addition, the adjustable carbon skeleton structure can effectively avoid irreversible damage when charge-discharge cycles. For Li-ion batteries, a specific capacity of 825 mAh g-1 is achieved after 100 cycles at 100 mA g-1, while for Na-ion batteries a specific capacity of 193 mAh g-1 is observed after 100 cycles at 100 mA g-1. Moreover, for Na-ion batteries, even at a high rate of 1000 mA g-1 the material delivers a specific capacity of 109.5 mAh g-1 after 3500 cycles.

Conducting polymer-coated MIL-101/S composite with scale-like shell structure for improving Li-S batteries.

Lithium-sulfur batteries are regarded as a promising energy storage system. However, they are plagued by rapid capacity decay, low coulombic efficiency, a severe shuttle effect and low sulfur loading in cathodes. To address these problems, effective carriers are highly demanded to encapsulate sulfur in order to extend the cycle life. Herein, we introduced a doped-PEDOT:PSS-coated MIL-101/S multi-core-shell structured composite. The unique structure of MIL-101, large specific area and conductive shell ensure high dispersion of sulfur in the composite and minimize the loss of polysulfides to the electrolyte. The doped-PEDOT:PSS-coated sulfur electrodes exhibited an increase in initial capacity and an improvement in rate characteristics. After 192 cycles at the current density of 0.1C, a doped-PEDOT:PSS-coated MIL-101/S electrode maintained a capacity of 606.62 mA h g-1, while the MIL-101/S@PEDOT:PSS electrode delivered a capacity of 456.69 mA h g-1. The EIS measurement revealed that the surface modification with the conducting polymer provided a lower resistance to the sulfur electrode, which resulted in better electrochemical behaviors in Li-S battery applications. Test results indicate that the MIL-101/S@doped-PEDOT:PSS is a promising host material for the sulfur cathode in the lithium-sulfur battery applications.