S. Cheng

Spinel MgAl2O4 modification on LiCoO2 cathode materials with the combined advantages of MgO and Al2O3 modifications for high-voltage lithium-ion batteries

In order to improve the electrochemical performance of LiCoO2 cathode in a high-voltage range of 3.0–4.5 V, spinel MgAl2O4 has been modified on the surface of LiCoO2 particle by a facile high-temperature solid state reaction. The structure and morphology of the MgAl2O4-modified LiCoO2 are investigated in comparison with the pristine, Al2O3-modified and MgO-modified LiCoO2. The MgAl2O4 modification is highly conformal and uniform just similar as the Al2O3 modification, while the MgO modification is not uniform. In terms of electrochemical performance as a high-voltage cathode material, the MgAl2O4-modified LiCoO2 delivers an initial discharge capacity of 184 mA h g−1 between 3.0 V and 4.5 V at 0.1C (1C-rate = 160 mA g−1) and a capacity retention of 96.8% after 70 cycles at 1C rate. There is a significant improvement on high-voltage cycling stability for the MgAl2O4-modified LiCoO2 since the capacity retention of the pristine LiCoO2 is only 38.7% after 70 cycles. Moreover, the MgAl2O4-modified LiCoO2 exhibits an enhanced rate capability. Compared with the Al2O3 modification and the MgO modification, spinel MgAl2O4 modification has the combined advantages of Al2O3 and MgO modifications on improving the electrochemical performance of the LiCoO2 cathode for high-voltage applications. The modified spinel MgAl2O4 layer can effectively protect the charged Li1−xCoO2 cathode from structural collapse and impede the oxidation decomposition of the electrolyte for the high-voltage application of LiCoO2.

Effects of porous structure of carbon hosts on preparation and electrochemical performance of sulfur/carbon composites for lithium–sulfur batteries

Three kinds of carbon hosts, Ketjenblack (KB, high surface area and porosity), black pearls 2000 (BP2000, high surface area and moderate porosity), and ordered mesoporous carbon nanospheres (OMCN, low surface area and porosity), have been used as conductive hosts in the sulfur/carbon (S/C) composite cathodes for lithium–sulfur (Li–S) batteries. To correlate the carbon properties (surface area and pore volume), the electrochemical performances of S/C composite cathodes with the same sulfur content (60 wt%) have been investigated in detail. S/KB and S/BP2000 composites with high surface porosity can provide more reactive sites for sulfur, which can result in increasing the utilization rate of sulfur, reducing the polarization, and improving the high-rate capability. Large pore volume can effectively capture the polysulfide species and improve easy passages for ion transport, which can promote long-term cycling stability and reduce the resistance of Li–S batteries.