锰氧化度对水钠锰矿电容性能的影响

The effect of Mn AOS on the supercapacitor performance of birnessite

高锰酸钾与盐酸在100℃回流反应制备层状水钠锰矿,改变盐酸用量调控水钠锰矿的锰平均氧化度(AOS),即Mn(Ⅳ)与Mn(Ⅲ)的相对含量。采用X射线衍射、扫描电镜、X射线吸收光谱等表征产物晶体结构、微观形貌、价态组成和键长等,考察锰平均氧化度对水钠锰矿理化性质与电容性能的影响。结果表明,随着盐酸用量增加,三维花球状水钠锰矿AOS降低,氧化度可调控为4.02,3.88和3.72,且组成花球的片层厚度有降低趋势,比表面积随之增大,层间K+和结晶水含量降低;水钠锰矿比电容量随氧化度升高而增大,其充放电过程中晶体内层间离子扩散速率显著影响电容性能。氧化度为4.02的水钠锰矿电化学性能最佳,比容量最大为232F/g,200周循环保持为222F/g,容量保持率为95.7%。

Layered birnessites were prepared by reflux reaction of concentrated hydrochloric acid and KMnO4at100 ℃.The Mn average oxidation state（AOS）,affected by the relative content of Mn（Ⅳ）and Mn（Ⅲ）,was controlled by adjusting the molar ratio of hydrochloric acid and KMnO4.The crystal structures,micromorphologies,compositions and bond length were characterized using X-ray diffractometer（XRD）,scanning electron microscope（SEM）,X-ray absorption spectroscopy（XAS）,and the influence of Mn AOS on the electrochemical performance of birnessites was studied by cyclic voltammetry and charge/discharge test.Results indicated that birnessites with three-dimension hierarchical microspheres composed of disk-shaped plates were formed.Mn AOSs were obtained as 4.02,3.88 and 3.72 when the molar ratios of concentrated hydrochloric acid and KMnO4 were controlled as 1.35∶1,1.66∶1,and 2∶1,respectively.The particle size of microspheres and the thickness of plates decreased,and the corresponding specific surface area increased with a decrease of Mn AOS.The measured interlayer distances of（001）crystal plane and the content of K＋and crystal water increased due to the increasing of Mn AOS.The supercapacitor performance increased with an increase in Mn AOS,and the interlayer distances of（001）crystal plane,the content of K＋and crystal water possibly played an important role in improving the electrochemical performance of birnessite.Birnessite with Mn AOS of 4.02 exhibited the best electrochemical performance with initial discharge capacity of 232F/g,and it decreased to 222F/g with retention rate about 95.7% after 200 cycles.