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A Theoretical study on the charge and discharge states of Na-ion battery cathode material, Na1+x FePO4 F
Journal of Computational Chemistry ( IF 3 ) Pub Date : 2018-10-20 , DOI: 10.1002/jcc.25582
Chikashi Shinagawa 1 , Yusuke Morikawa 1 , Shin-ichi Nishimura 1 , Hiroshi Ushiyama 1 , Atsuo Yamada 1 , Koichi Yamashita 1
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Na2FePO4F is a promising cathode material for a Na‐ion battery because of its high electronic capacity and good cycle performance. In this work, first principle calculations combined with cluster expansion and the Monte Carlo method have been applied to analyze the charge and discharge processes of Na2FePO4F by examining the voltage curve and the phase diagram. As a result of the density functional theory calculation and experimental verification with structural analysis, we found that the most stable structure of Na1.5FePO4F has the P21/b11 space group, which has not been reported to date. The estimated voltage curve has two clear plateaus caused by the two‐phase structure composed of P21/b11 Na1.5FePO4F and Pbcn Na2FePO4F or Na1FePO4F and separated along the c‐axis direction. The phase diagram shows the stability of the phase‐separated structure. Considering that Na2FePO4F has diffusion paths in the a‐ and c‐axis directions, Na2FePO4F has both innerphase and interphase diffusion paths. We suggest that the stable two‐phase structure and the diffusion paths to both the innerphase and interphases are a key for the very clear plateau. We challenge to simulate a nonequilibrium state at high rate discharge with high temperature by introducing a coordinate‐dependent chemical potential. The simulation shows agreement with the experimental discharge curve on the disappearance of the two plateaus. © 2018 Wiley Periodicals, Inc.

中文翻译:

钠离子电池正极材料Na1+x FePO4 F充放电状态的理论研究

Na2FePO4F 具有高电子容量和良好的循环性能,是一种很有前途的钠离子电池正极材料。在这项工作中,第一性原理计算结合簇扩展和蒙特卡罗方法,通过检查电压曲线和相图,分析了 Na2FePO4F 的充放电过程。作为密度泛函理论计算和结构分析实验验证的结果,我们发现 Na1.5FePO4F 最稳定的结构具有 P21/b11 空间群,目前尚未见报道。估计的电压曲线有两个明显的平台,这是由 P21/b11 Na1.5FePO4F 和 Pbcn Na2FePO4F 或 Na1FePO4F 组成的两相结构引起的,沿 c 轴方向分离。相图显示了相分离结构的稳定性。考虑到 Na2FePO4F 在 a 轴和 c 轴方向有扩散路径,Na2FePO4F 既有内相扩散路径,也有相间扩散路径。我们认为稳定的两相结构和到内相和中间相的扩散路径是非常清晰的平台的关键。我们通过引入依赖于坐标的化学势来挑战在高温下高速放电时模拟非平衡状态。模拟显示与实验放电曲线在两个平台消失方面的一致性。© 2018 Wiley Periodicals, Inc. 我们认为稳定的两相结构和到内相和中间相的扩散路径是非常清晰的平台的关键。我们通过引入依赖于坐标的化学势来挑战在高温下高速放电时模拟非平衡状态。模拟显示与实验放电曲线在两个平台消失方面的一致性。© 2018 Wiley Periodicals, Inc. 我们认为稳定的两相结构和到内相和中间相的扩散路径是非常清晰的平台的关键。我们通过引入依赖于坐标的化学势来挑战在高温下高速放电时模拟非平衡状态。模拟显示与实验放电曲线在两个平台消失方面的一致性。© 2018 Wiley Periodicals, Inc.
更新日期:2018-10-20
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