水溶液中掺铬层状二氧化锰可充性研究

由高温分解KMnO₄制备层状K-birnessite前驱体, 再经过离子交换反应制备Cr-birnessite. 在2.5 mol/L LiOH水溶液中研究了Cr-birnessite电极的可充性. 据AAS测试和锰的价态分析得Cr-birnessite的分子式为Cr_0.26Mn_0.84O_2＋0.04. SEM显示Cr-birnessite为片状颗粒, XRD分析表明其层状结构在充放电前后没有明显变化. 恒电流充放电实验表明在2.5 mol/L LiOH水溶液中以1 C大电流速率对Cr-birnessite进行全充全放循环可达70次而保持初始容量的93%, 显示了良好的循环可逆性. AAS表明在充放电过程中材料中的铬离子没有脱嵌, Li^＋脱嵌/嵌入. 循环伏安曲线表明在大约 －0.3和0 V出现两个氧化峰, 在－0.1 V左右出现一个还原峰, 循环20周电流大小没有明显变化. 利用恒电位阶跃法测得Li^＋在Cr-birnessite 中的扩散系数平均值为1.57×10^－10 cm²·s^－1 .

Investigation of the Rechargeability of the Cr-birnessite in Aqueous Solution

The Cr-birnessite was prepared by ion exchange from K-birnessite, which was synthesized by calcination of KMnO₄. Measurement methods of scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), atomic absorption spectrometry (AAS), slow-scanning cyclic voltammetric and galvanostatic discharge/charge characteristics of the Cr-birnessite were applied. Potentiostatic method was used for the determination of a chemical diffusion coefficient D. XRD patterns indicate that Cr-birnessite has layered structure. Slow-scanning voltammograms exhibit single peak occurring in the range of －0.2 to 0 V on discharge and two peaks at about －0.3 and 0 V on charge. The galvanostatic discharge/charge curves indicate that the Cr-birnessite has better rechargeability at a high discharge/charge rate. Li^＋can reversibly intercalate into and de-intercalate from the Cr-birnessite during discharge and charge. The average value of the chemical diffusion coefficient D of Li^＋ intercalated into the Cr-birnessite is 1.57×10^－10cm²·s^－1.