Xi Yuming, Lu Yangcheng
State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.
ACS Appl Mater Interfaces. 2022 Aug 31;14(34):39022-39030. doi: 10.1021/acsami.2c07779. Epub 2022 Aug 18.
In this work, for the performance enhancement of iron hexacyanoferrate, an electrochemically active Mn-doped iron hexacyanoferrate cathode is fabricated via a bottom-up approach. It is found that the pre-treatment of interstitial water and appropriate Mn doping are two keys to achieving higher capacity and higher stability. The interstitial water has a trade-off effect between the alleviation of volume expansion upon Na (de)intercalation and the retardation of Na-ion diffusion. The moisture-tailored iron hexacyanoferrate with appropriate Mn doping exhibits a high initial Coulombic efficiency of 94.8%, enhanced capacity and rate performance, and excellent cycling stability. These results benefit from the fact that the extraction/insertion of Na ions from/into the lattice via a solid-solution mechanism correspond to both the slight volume expansion and fast sodium diffusion rate; otherwise, the removal of interstitial water and a higher Mn content might lead to poor cycling stability due to excessive volume expansion resulting from rhombohedral to cubic phase transformation. Finally, the less demand on the control of air humidity for the fabrication of electrodes and the potential for the full cell coupled with hard carbon are also demonstrated, which shows great potential for practical applications.
在这项工作中，为了提高铁氰化铁的性能，通过自下而上的方法制备了一种具有电化学活性的锰掺杂铁氰化铁阴极。研究发现，间隙水的预处理和适当的锰掺杂是实现更高容量和更高稳定性的两个关键因素。间隙水在缓解钠嵌入/脱嵌时的体积膨胀和阻碍钠离子扩散之间存在权衡效应。经过水分定制且掺杂适当锰的铁氰化铁表现出94.8%的高初始库仑效率、增强的容量和倍率性能以及出色的循环稳定性。这些结果得益于通过固溶体机制从晶格中提取/插入钠离子既对应轻微的体积膨胀又对应快速的钠扩散速率这一事实；否则，间隙水的去除和较高的锰含量可能会由于菱面体到立方相转变导致的过度体积膨胀而导致循环稳定性较差。最后，还展示了电极制备过程中对空气湿度控制的较低要求以及与硬碳耦合用于全电池的潜力，这显示出其在实际应用中的巨大潜力。
