Shakoor Rana A, Park Chan Sun, Raja Arsalan A, Shin Jaeho, Kahraman Ramazan
Center for Advanced Materials (CAM), Qatar University, Doha 2713, Qatar.
Phys Chem Chem Phys. 2016 Feb 7;18(5):3929-35. doi: 10.1039/c5cp06836c. Epub 2016 Jan 14.
The development of secondary batteries based on abundant and cheap elements is vital. Among various alternatives to conventional lithium-ion batteries, sodium-ion batteries (SIBs) are promising due to the abundant resources and low cost of sodium. While there are many challenges associated with the SIB system, cathode is an important factor in determining the electrochemical performance of this battery system. Accordingly, ongoing research in the field of SIBs is inclined towards the development of safe, cost effective cathode materials having improved performance. In particular, pyrophosphate cathodes have recently demonstrated decent electrochemical performance and thermal stability. Herein, we report the synthesis, electrochemical properties, and thermal behavior of a novel Na2Fe0.5Mn0.5P2O7 cathode for SIBs. The material was synthesized through a solid state process. The structural analysis reveals that the mixed substitution of manganese and iron has resulted in a triclinic crystal structure (P1[combining macron] space group). Galvanostatic charge/discharge measurements indicate that Na2Fe0.5Mn0.5P2O7 is electrochemically active with a reversible capacity of ∼80 mA h g(-1) at a C/20 rate with an average redox potential of 3.2 V. (vs. Na/Na(+)). It is noticed that 84% of initial capacity is preserved over 90 cycles showing promising cyclability. It is also noticed that the rate capability of Na2Fe0.5Mn0.5P2O7 is better than Na2MnP2O7. Ex situ and CV analyses indicate that Na2Fe0.5Mn0.5P2O7 undergoes a single phase reaction rather than a biphasic reaction due to different Na coordination environment and different Na site occupancy when compared to other pyrophosphate materials (Na2FeP2O7 and Na2MnP2O7). Thermogravimetric analysis (25-550 °C) confirms good thermal stability of Na2Fe0.5Mn0.5P2O7 with only 2% weight loss. Owing to promising electrochemical properties and decent thermal stability, Na2Fe0.5Mn0.5P2O7, can be an attractive cathode for SIBs.
开发基于丰富且廉价元素的二次电池至关重要。在传统锂离子电池的各种替代方案中，钠离子电池（SIBs）因其钠资源丰富且成本低而颇具前景。虽然SIB系统存在诸多挑战，但正极是决定该电池系统电化学性能的一个重要因素。因此，SIBs领域目前的研究倾向于开发性能更优、安全且具成本效益的正极材料。特别是，焦磷酸盐正极最近展现出了良好的电化学性能和热稳定性。在此，我们报告一种用于SIBs的新型Na2Fe0.5Mn0.5P2O7正极的合成、电化学性质及热行为。该材料通过固态法合成。结构分析表明，锰和铁的混合取代导致了三斜晶体结构（P1[组合宏]空间群）。恒电流充放电测量表明，Na2Fe0.5Mn0.5P2O7具有电化学活性 在C/20倍率下可逆容量约为80 mA h g(-1)，平均氧化还原电位为3.2 V（相对于Na/Na(+)）。值得注意的是，在90次循环后仍保留了84%的初始容量，显示出良好的循环稳定性。还注意到Na2Fe0.5Mn0.5P2O7的倍率性能优于Na2MnP2O7。非原位和循环伏安分析表明，与其他焦磷酸盐材料（Na2FeP2O7和Na2MnP2O7）相比，由于不同的Na配位环境和不同的Na位点占有率，Na2Fe0.5Mn0.5P2O7经历单相反应而非双相反应。热重分析（25 - 550 °C）证实Na2Fe0.5Mn0.5P2O7具有良好的热稳定性，重量损失仅为2%。由于具有良好的电化学性能和热稳定性，Na2Fe0.5Mn0.5P2O7有望成为SIBs颇具吸引力的正极材料。
