Constructing Multi-Electron Reactions by Doping Mn²⁺ to Increase Capacity and Stability in K_3.2V_2.8Mn_0.2(PO₄)₄/C of...

Vanadium-based phosphate cathode materials (e.g., K₃V₂(PO₄)₃) have attracted widespread concentration in cathode materials in potassium-ion batteries owing to their stable structure but suffer from low capacity and poor conductivity. In this work, an element doping strategy is applied to promote its electrochemical performance so that K_3.2V_2.8Mn_0.2(PO₄)₄/C is prepared via a simple sol-gel method. The heterovalent Mn²⁺ is introduced to stimulated multiple electron reactions to improve conductivity and capacity, as well as interlayer spacing. Galvanostatic intermittent titration technique (GITT) and in situ X-ray diffraction results further confirm that Mn-doping in the original electrode can obtain superior electrode process kinetics and structural stability. The prepared K_3.2V_2.8Mn_0.2(PO₄)₄/C exhibits a high-capacity retention of 80.8% after 1 500 cycles at 2 C and an impressive rate capability, with discharge capacities of 87.6 at 0.2 C and 45.4 mA h g^-1 at 5 C, which is superior to the majority of reported vanadium-based phosphate cathode materials. When coupled K_3.2V_2.8Mn_0.2(PO₄)₄/C cathode with commercial porous carbon (PC) anode as the full cell, a prominent energy density of 175 Wh kg^-1 is achieved based on the total active mass. Overall, this study provides an effective strategy for meliorating the cycling stability and capacity of the polyanion cathodes for KIB.