Synthesis and characterization of Na0.44MnO2 nanorods/graphene composite as cathode materials for sodium-ion batteries

Na0.44MnO2 nanorods have been prepared by a hydrothermal method.The experimental parameters have been systematically investigated and optimized.The results show that Na0.44MnO2 nanorods obtained via the hydrothermal treatment at 200℃for 16 h show the best electrochemical properties,which deliver the high initial discharge capacity of 110.7 mA·h/g at 50 mA/g in potential window 2.0-4.0 V.To further improve their electrochemical properties,a ball milling process with graphene has been carried out to obtain Na0.44MnO2/graphene composite.The initial discharge capacity of Na0.44MnO2/graphene composite is 106.9 mA·h/g at a current density of 50 mA/g.After 100 cycles,the residual discharge capacity is 91.8 mA·h/g and the capacity retention rate is 85.9%,which is much higher than that of pristine Na0.44MnO2 nanorods(74.7%)at the same condition.What is more,when the current density reaches 500 and 1000 mA/g,the corresponding discharge capacities of Na0.44MnO2/graphene composite are about 89 and 78 mA·h/g,respectively,indicating outstanding rate capability.

Preparation of sodium manganate from low-grade pyrolusite by alkaline predesilication-fluidized roasting technique

Low concentration alkaline leaching was used for predesilication treatment of low-grade pyrolusite. The effects of initial NaOH concentration, liquid-to-solid ratio, leaching temperature, leaching time and stirring speed on silica leaching rate were investigated and the kinetics of alkaline leaching process was studied. The results show that silica leaching rate reached 91.2% under the conditions of initial NaOH concentration of 20%, liquid-to-solid ratio of 4：1, leaching temperature of 180 ℃, leaching time of 4 h and stirring speed of 300 r/min. Shrinking-core model showed that the leaching process was controlled by the chemical surface reaction with activation energy Ea of 53.31 k J/mol. The fluidized roasting conditions for preparation of sodium manganate were optimized by the orthogonal experiments using the desiliconized residue. The conversion rate of sodium manganate was obtained to be 89.7% under the conditions of silica leaching rate of 91.2%, NaOH/MnO2 mass ratio of 3：1, roasting temperature of 500 ℃ and roasting time of 4 h, and it increased with the increase of silicon leaching rate.

Enhancing storage performance of P2-type Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)cathode materials by Al_(2)O_(3)coating

The P2-type Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were synthesized by an ultrasonic spray pyrolysis followed by solid-state sintering method.The structures,morphologies and electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials were characterized thoroughly by means of X-ray diffractometer,scanning electron microscope and electrochemical charge/discharge instruments.Moreover,a thin layer of Al_(2)O_(3),which was formed on the surface of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2),can enhance the storage performance by preventing the formation of Na_(2)CO_(3)·H_(2)O,which is believed to enhance the electrochemical performances of Na_(2/3)Fe_(1/2)Mn_(1/2)O_(2)materials.This facile surface modification method may pave a way to synthesize advanced cathode materials for sodium-ion batteries.

Galena-pyrolusite co-extraction in sodium chloride solution and its electrochemical analysis

The co-extraction behavior of galena-pyrolusite in a sodium chloride solution and the electrochemical mechanism of this process were investigated,and some factors affecting the leaching rate of Pb and Mn were optimized.The results show that all the factors such as the concentration of NaCl,HCl and pyrolusite ore,reaction time,temperature,adding times of HCl,affect the leaching rate of Pb.The main affecting factors are the concentration of NaCl,reaction time and temperature.The Tafel polarization curves and EIS plots of the galena and pyrolusite in the NaCl solution demonstrate that during the oxidation process of galena mineral electrode,film forms on the galena surface,which prevents galena from deeper oxidation.However,the film resistance can be greatly reduced in the presence of sodium chloride,thus promoting the reaction rate of galena.

Bio-solubilization of Chinese lignite I:extra-cellular protein analysis

A white rot fungus strain, Trichoderma sp.AH, was isolated from rotten wood in Fushun and used to study the mechanism of lignite bio-solubilization.The results showed that nitric acid pretreated Fushun lignite was solubilized by T.sp.AH and that extracellular proteins from T.sp.AH were correlated with the lignite bio-solubilization results.In the presence of Fushun lignite the extracellular protein concentration from T.sp.AH was 4.5 g/L while the concentration was 3 g/L in the absence of Fushun lignite.Sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE) of the extracellular proteins detected at least four new protein bands after the T.sp.AH had solubilized the lignite.Enzyme color reactions showed that extracellular proteins from T.sp.AH mainly consisted of phenol-oxidases, but that lignin decomposition enzymes such as laccase, peroxidase and manganese peroxidases were not present.