Optimizing Electronic Structure to Achieve High-Capacity and Long-Life Layered Oxide Cathode for Potassium-Ion Batteries.

Abstract

Layered Mn-based oxide cathodes demonstrate great potential for application in potassium-ion batteries. However, issues such as Jahn-Teller distortion of Mn and significant volume changes during K⁺ intercalation/removal severely limit their practical use. To address these challenges, we successfully synthesize the cathode material K_0.7Fe_0.3Ni_0.15Mg_0.03Ti_0.02Mn_0.5O₂ (KFNMTMO) by introducing low-valence ions and incorporating active metal elements. The results show that the introduction of low-valence ions raises the average oxidation state of Mn to approximately +4, causing the projected density of states of Mn to shift above the Fermi level. This effectively suppresses the redox activity of Mn, making it primarily responsible for stabilizing layered structure. Meanwhile, electronic structure optimization considerably activates the redox couples of other active elements such as Ni²⁺/Ni³⁺ and Fe³⁺/Fe⁴⁺. This synergistic effect not only alleviates Jahn-Teller distortion but also, through the addition of the less electronegative Mg²⁺ ions, markedly enhances the orbital hybridization between transition metals and oxygen atoms, further improving the stability of crystal lattice. Consequently, the KFNMTMO cathode exhibits excellent electrochemical performance, achieving a reversible capacity of 114.3 mAh g^-1 at 20 mA g^-1, an energy density of 328 Wh kg^-1, and remarkable cycling stability with a capacity retention of 81.5% after 800 cycles.