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

Abstract

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 a 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, we propose a repair method that significantly reduces the VFeCN content in potassium manganese hexacyanoferrate (KMHCF) enabled by the reducibility of sodium citrate and remove of ligand H2O at high temperature (KMHCF‐H). The KMHCF‐H obtained at 90°C contain 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 layer at the surface, 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.This article is protected by copyright. All rights reserved

Recent advances in rational design for high-performance potassium-ion batteries

“…The wide channel structure of PBAs enables facile transport of large K + ions for electrochemically reversible K + de/intercalation. 91,238–240…”

“…23d). Li et al 91 found that the KMnHCF cathode with lower vacancy concentration (KMHCF-H) is more likely to form a KF-rich CEI than the KMHCF cathode with higher vacancy concentration (KMHCF-C). Time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated that for the KMnHCF-C electrode, TEP was preferentially decomposed (Fig.…”