Sundaram Manickam Minakshi, Watcharatharapong Teeraphat, Chakraborty Sudip, Ahuja Rajeev, Duraisamy Shanmughasundaram, Rao Penki Tirupathi, Munichandraiah Nookala
Department of Chemistry, Murdoch University, Murdoch, WA 6150, Australia.
Department of Physics and Astronomy, Uppsala University, Sweden.
Dalton Trans. 2015 Dec 14;44(46):20108-20. doi: 10.1039/c5dt03394b.
Energy storage devices based on sodium have been considered as an alternative to traditional lithium based systems because of the natural abundance, cost effectiveness and low environmental impact of sodium. Their synthesis, and crystal and electronic properties have been discussed, because of the importance of electronic conductivity in supercapacitors for high rate applications. The density of states of a mixed sodium transition metal phosphate (maricite, NaMn(1/3)Co(1/3)Ni(1/3)PO4) has been determined with the ab initio generalized gradient approximation (GGA)+Hubbard term (U) method. The computed results for the mixed maricite are compared with the band gap of the parent NaFePO4 and the electrochemical experimental results are in good agreement. A mixed sodium transition metal phosphate served as an active electrode material for a hybrid supercapacitor. The hybrid device (maricite versus carbon) in a non-aqueous electrolyte shows redox peaks in the cyclic voltammograms and asymmetric profiles in the charge-discharge curves while exhibiting a specific capacitance of 40 F g(-1) and these processes are found to be quasi-reversible. After long term cycling, the device exhibits excellent capacity retention (95%) and coulombic efficiency (92%). The presence of carbon and the nanocomposite morphology, identified through X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, ensures the high rate capability while offering possibilities to develop new cathode materials for sodium hybrid devices.
基于钠的储能装置因其钠的天然丰度、成本效益和低环境影响，已被视为传统锂基系统的替代品。由于电子导电性在高速应用超级电容器中的重要性，人们已对其合成、晶体和电子性质进行了讨论。采用从头算广义梯度近似（GGA）+哈伯德项（U）方法确定了混合钠过渡金属磷酸盐（镁铁石，NaMn(1/3)Co(1/3)Ni(1/3)PO4）的态密度。将混合镁铁石的计算结果与母体NaFePO4的带隙进行了比较，电化学实验结果与之吻合良好。一种混合钠过渡金属磷酸盐用作混合超级电容器的活性电极材料。在非水电解质中的混合装置（镁铁石对碳）在循环伏安图中显示出氧化还原峰，在充放电曲线中显示出不对称曲线，同时表现出40 F g(-1)的比电容，并且发现这些过程是准可逆的。经过长期循环后，该装置表现出优异的容量保持率（95%）和库仑效率（92%）。通过X射线光电子能谱（XPS）和透射电子显微镜（TEM）研究确定的碳的存在和纳米复合形态，确保了高倍率性能，同时为开发用于钠混合装置的新型阴极材料提供了可能性。
