普鲁士蓝类似物由于其宽敞的三维骨架而受到极大的关注,高理论比容量,简易合成程序,和高成本效益是钠离子电池(SIB)中正极材料最有前途的候选材料之一。尽管如此,实际的具体能力,特别是在大电流下,由于离子扩散缓慢,特别脆弱。在这项研究中,采用Ni取代和形成水配位Fe的策略来降低晶体场能量并提高活性低自旋(LS)Fe含量,这导致了电容性钠存储机制,在高电流密度下产生相当大的比容量。PW-325@2NiFe-55在50C时的比容量为95mAhg-1,在0.5C下的容量保持率为72.5%。此外,在5°C下500次循环后,它保持其初始比容量的80.2%。此外,提出了高自旋(HS)Fe的联合扩散控制和电容机制的假设,并通过电位测试进行了验证,operando57FeMössbauer光谱学,和非原位XRD,这为提高SIB的电化学性能提供了新的视野。
Prussian blue analogues receive tremendous attention owing to their spacious three-dimensional skeleton, high theoretical specific capacity, facile synthesis procedure, and high cost-effectiveness as among the most promising candidates for cathode materials in sodium-ion batteries (SIBs). Nonetheless, the practical specific capacity, especially under high current, is particularly frail due to the sluggish ion diffusion. In this study, the strategy of Ni substitution and formation of water-coordinated Fe is applied to lower the crystal field energy and elevate the active low-spin (LS) Fe content, which leads to a capacitive sodium storage mechanism, resulting in a substantial specific capacity under high current density. The delivered specific capacity of PW-325@2NiFe-55 is 95 mAh g-1 at 50 C, which is 72.5% capacity retention of the one at 0.5 C. Also, it maintains 80.2% of its initial specific capacity after 500 cycles at 5 C. Furthermore, a hypothesis of a joint diffusion-controlled and capacitive mechanism for high-spin (HS) Fe and a mere capacitive mechanism for LS Fe is put forward and verified through potentiastatic tests, operando 57Fe Mössbauer spectroscopy, and ex situ XRD, which provides a new horizon to enhance the electrochemical performance for SIBs.