New Dimorphs of Na5V(PO4)(2)F-2 as an Ultrastable Cathode Material for Sodium-Ion Batteries
New Dimorphs of Na5V(PO4)(2)F-2 as an Ultrastable Cathode Material for Sodium-Ion Batteries
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新型Na5V(PO4)(2)F-2二晶型作为钠离子电池超稳定正极材料
DOI：
10.1021/acsaem.9b02248
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发表时间：
2020
影响因子：
6.4
通讯作者：
Yong Yang
中科院分区：
文献类型：
--
作者：
Ziteng Liang;Xiaofeng Zhang;Rui Liu;Gregorio F. Ortiz;Guiming Zhong;Yuxuan Xiang;Shijian Chen;Jinxiao Mi;Shunqing Wu;Yong Yang
本文首次采用简便的合成方法合成了一种新型钠离子电池氟磷酸盐正极材料Na 5V（PO 4）2F 2。X射线衍射分析表明该新型材料采用两种空间群（即，双晶型）：高温（800 °C）下为斜方晶型（空间群（SG）：Pbca），低温（600 °C）下为三方晶型（SG：P3）。它们都具有层状结构，可以可逆地插入（脱）一个钠与V3+/V4+氧化还原对。由于氟的“感应效应”，新的二晶型物还表现出高的工作电压，即，3.4 V的三角形Na 5V（PO 4）2F 2（t-NVPF）和3.5 V的正交Na 5V（PO 4）2F 2（o-NVPF）。此外，它们都表现出出色的循环稳定性，在136 mA g-1下，o-NVPF/C和t-NVPF在1000次循环后分别显示出86.5%和92.6%的高容量保持率。基于非原位XRD和DFT计算，NVPF化合物如t-NVPF的优异循环性能归因于其稳健的聚阴离子骨架，在可逆Na+（脱）插层过程中体积变化较小。
In this work, a new fluorophosphate cathode material Na5V(PO4)2F2for sodium-ion batteries is synthesized by a facile synthetic strategy for the first time. X-ray diffraction analyses indicate that the novel material adopts two space groups (i.e., dimorphs): an orthorhombic form (space group (SG):Pbca) at high temperature (800 °C) and a trigonal form (SG:P3) at low temperature (600 °C). Both of them have a layered structure and could reversibly (de)intercalate one sodium with a V3+/V4+redox couple. The new dimorphs also exhibit a high operating voltage due to the “induction effect” of fluorine, i.e., 3.4 V for trigonal Na5V(PO4)2F2(t-NVPF) and 3.5 V for orthorhombic Na5V(PO4)2F2(o-NVPF), respectively. In addition, they both exhibit outstanding cyclic stability, showing high capacity retentions of 86.5% and 92.6% after 1000 cycles for o-NVPF/C and t-NVPF at 136 mA g–1, respectively. On the basis of ex situ XRD and DFT calculations, the excellent cycling performance of NVPF compounds such as t-NVPF is attributed to their robust polyanion framework, with fewer volume changes during reversible Na+(de)intercalation processes.