Interior‐Confined Vacancy in Potassium Manganese Hexacyanoferrate for Ultra‐Stable Potassium‐Ion Batteries

• Published in: Advanced materials (Weinheim) 2024-04, Vol.36 (15), p.e2310428-n/a
• Main Authors: Li, Xiaoxia, Guo, Tianqi, Shang, Yang, Zheng, Tian, Jia, Binbin, Niu, Xiaogang, Zhu, Yujie, Wang, Zhongchang
• Format: Article
• Language: English
• Subjects: Cathodes; Cathodic dissolution; Cycles; Dissolution; Electrode materials; Electrolytes; Fe(CN)6 vacancies; High temperature; K2Mn[Fe(CN)6]; Manganese; Mn dissolution; Potassium; potassium‐ion batteries; Rechargeable batteries; Sodium citrate; Surface structure; surface vacancy repairs
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202310428

Metal hexacyanoferrates (HCFs) are viewed as promising cathode materials for potassium‐ion batteries (PIBs) because of their high theoretical capacities and redox potentials. However, the development of an HCF cathode with high cycling stability and voltage retention is still impeded by the unavoidable Fe(CN)6 vacancies (VFeCN) and H2O in the materials. Here, a repair method is proposed that significantly reduces the VFeCN content in potassium manganese hexacyanoferrate (KMHCF) enabled by the reducibility of sodium citrate and removal of ligand H2O at high temperature (KMHCF‐H). The KMHCF‐H obtained at 90 °C contains only 2% VFeCN, and the VFeCN is concentrated in the lattice interior. Such an integrated Fe–CN–Mn surface structure of the KMHCF‐H cathode with repaired surface VFeCN allows preferential decomposition of potassium bis(fluorosulfonyl)imide (KFSI) in the electrolyte, which constitutes a dense anion‐dominated cathode electrolyte interphase (CEI) , inhibiting effectively Mn dissolution into the electrolyte. Consequently, the KMHCF‐H cathode exhibits excellent cycling performance for both half‐cell (95.2 % at 0.2 Ag−1 after 2000 cycles) and full‐cell (99.4 % at 0.1 Ag−1 after 200 cycles). This thermal repair method enables scalable preparation of KMHCF with a low content of vacancies, holding substantial promise for practical applications of PIBs. A surface repair strategy is proposed to reduce the content of Fe(CN)6 vacancies (VFeCN) in potassium manganese hexacyanoferrate (KMHCF). KMHCF with 2% VFeCN is obtained at 90 °C, and VFeCN is mainly concentrated in the lattice interior. The eliminated surface VFeCN can inhibit the Mn2+ dissolution into the electrolyte, resulting in excellent cycling performance in potassium ion batteries.