Stabilization of layered-type potassium manganese oxide cathode with fluorine treatment for high-performance K-ion batteries

Layered potassium manganese oxides (KxMnO2) have been widely investigated as potential cathode materials for K-ion batteries owing to their high capacity and low material cost. However, the KxMnO2 cathodes generally suffer from unsatisfactory cycle life due to Mn dissolution into the electrolyte triggered by acidic HF corrosion and structural stress at the particle surface during cycling. In this study, we introduce an efficient strategy to stabilize the aggressive chemistry between the organic electrolyte solution and the P′3-type K0·6MnO2 (KMO) cathode surface through fluorine treatment. KF-coated P′3-type K0.6MnO1.97F0.03 (KMOF-7) is prepared by introducing 7 mol% of ammonium fluoride (NH4F) during a pyro-synthesis of K0·6MnO2. The partial substitution of F to oxygen atom narrows the interlayer spacing, which helps to reduce the insertion of electrolyte molecules into the crystal structure; meanwhile, the formation of KF coating layer on the cathode surface can suppress the Mn dissolution by protecting KMOF-7 from reacting with HF in the electrolyte solution during charge–discharge processes. This strategy can relieve the structural stress and stabilize the interfacial stability of KMOF-7, thereby, facilitating K+ transportation and depress the charge transfer resistance upon cycling. The KMOF-7 cathode demonstrates the significantly improved cycling stability and power capability compared to KMO.