钠离子电池新型Cu基隧道型氧化物正极材料研究

成本较为低廉的钠离子电池成为储能领域的新秀,备受关注.以Na₂CO₃,CuO,Fe₂O₃,MnO₂和TiO₂为原料,通过简单的固相反应法合成了一系列新型Cu基隧道结构化合物.通过X射线衍射（XRD）、扫描电子显微镜（SEM）和电化学性能测试对所得样品的结构、形貌以及电化学性能进行了表征.XRD结果表明材料结构与Na_0.44MnO₂一样为隧道结构,空间群为pbam.室温下的电化学性能测试表明Mn替代的样品在1.5~4.1 V的范围内表现出了90 mAh/g的比容量,循环稳定,倍率性能较好,1C容量保持率仍为74%.XPS结果验证了Cu在充放电过程中参与了变价.原位XRD结果表明Na_0.66Cu_0.17Mn_0.33Ti_0.5O₂电极材料在1.5~4.1 V的范围内可以保持稳定的隧道型结构.本工作首次报道了Cu在隧道型结构材料中的变价行为,为进一步设计隧道结构的材料以及钠离子电池正极材料提供新思路.     

A High-Temperature β-Phase NaMnO_2 Stabilized by Cu Doping and Its Na Storage Properties

The high-temperature β-phase NaMnO_2 is a promising material for Na-ion batteries(NIBs) due to its high capacity and abundant resources. However, the synthesis of phase-pure -NaMnO_2 is burdensome and costineffective because it needs to be sintered under oxygen atmosphere at high temperature and followed by a quenching procedure. Here we first report that the pure β phase can be stabilized by Cu-doping and easily synthesized by replacing a proportion of Mn with Cu via a simplified process including sintering in air and cooling to room temperature naturally. Based on the first-principle calculations, the band gap decreases from 0.7 eV to 0.3 eV, which indicates that the electronic conductivity can be improved by Cu-doping. The designed -NaCu_(0.1)Mn_(0.9)O_2 is applied as cathode in NIBs, exhibiting an energy density of 419 Wh/kg and better performance in terms of rate capability and cycling stability than those in the undoped case.