Study On Properties Of Fes₂ Prepared By Hydrothermal Method

Effects of desulfurization, acid treatment and lithium-doping on the structure, morphology and discharge performance of FeS2 prepared by hydrothermal method were systematically studied. The structure and morphology were characterized by TG-DTA, XRD and SEM; and the discharge performance was analyzed by constant-current discharge test. The effect of different desulfurization methods on discharge performance, the variation of its discharge performance after treated by different concentrations of acid, and the improvement of discharge voltage depression after doping of LiOH?H₂O were especially studied in this paper.It was found that both washing desulfurization and heat-treatment desulfurization could obtain pyrite with good discharge performance. Washing with chloroform and heat-treatment method were used to purify FeS2. The results showed that the heat-treatment sample achieved a high open-circuit voltage of 2.67V, higher than the theoretical value, and a good discharge platform whosedischarge capacity could reach 94.7% of the theoretical specific capacity.However washed sample obtained a relatively low open-circuit voltage, and an unstable discharge plateau whose discharge capacity could reach as high as 886.5mAh/g, 99.6 % of the theoretical specific capacity.XRD and SEM results showed that FeS2 after long-term storage was decomposed, resulting in bulk impurities, such as elemental sulfur and a small amount of iron oxide which could be reduced after treated by sulfuric acid and hydrochloric acid, thus leading to its improved discharge performance. The sample treated by 2.63mol/L sulfuric acid showed a discharge capacity of 763.4mAh/g, 121.4 mAh/g higher than the untreated sample. And the discharge capacity of sample treated by 1.33 mol/L hydrochloric acid was as high as 784.0 mAh/g, 142.0 mAh/g higher than the untreated sample.Doping LiOH?H₂O and following heat-treatment could effectively improve the discharge platform depression problem. After treated by 1/3mol/L LiOH? H₂O, the sample exhibited a discharge capacity of 808.8 mAh/g, with a sag voltage of 20mV, 290mV higher than the untreated sample. While after heat-treatment at 450℃, the voltage sag was significantly reduced, and the discharge capacity could reach 859.3mAh/g, 50.5 mAh/g higher than the untreated sample.