Deye Sun

Good Low-Temperature Properties of Nitrogen-Enriched Porous Carbon as Sulfur Hosts for High-Performance Li–S Batteries

Despite the increased attention devoted to exploring cathode construction based on various nitrogen-enriched carbon scaffolds at room temperature, the low-temperature behaviors of Li-S cathodes have yet to be studied. Herein, we demonstrate the good low-temperature electrochemical performances of nitrogen-enriched carbon/sulfur composite cathodes. Electrochemical evaluation indicates that a reversible capacity of 368 mAh g(-1) (0.5 C) over 100 cycles is achieved at -20 °C. After returning to 25 °C, a capacity of 620 mAh g(-1) (0.5 C) is achieved over 350 cycles with a low-capacity attenuation rate (0.071% per cycle) and an initial capacity of 1151 mAh g(-1) (0.1C). This positive electrochemical property was speculated to result from the good surface chemistry of the various amine groups in the nitrogen-enriched carbon materials with enhanced polysulfide immobilization.

Preparation and evaluation of a separator with an asymmetric structure for lithium-ion batteries

The different electrochemical characteristics stemming from the cathode and anode of lithium-ion batteries may have different effects on the surface properties of contacted separators. Herein, a series of composite separators with an asymmetric porous structure are fabricated by a one-step phase inversion method coupled with the settling of SiO2 nanoparticles due to gravity within the poly(vinylidenefluoride-co-hexafluoropylene) (PVDF-HFP) polymer matrix. The unique asymmetric porous separators are composed of a PVDF-HFP-rich layer with high porosity on the front surface, which is in contact with the air, and a SiO2-rich layer on the back surface, which is in contact with the substrate. Besides their excellent thermal stability and high safety towards fire, these asymmetric porous separators result in a high discharge capacity, enhanced cycling performance and excellent rate capability when assembled with a LiNi0.5Mn1.5O4 cathode in coin cells, indicating that the asymmetric porous composite separators could be a promising candidate to improve the performance of lithium-ion batteries.