A Novel Ternary Li-Rich Li₄Fe_0.5Mn_0.5V(PO₄)₃ Cathode for Ultra-High-Capacity Li-Ion Batteries with Potential Far Beyond LFP via Multi-Electron Reaction

LiFePO₄ (LFP) has successfully realized large-scale applications due to excellent stability. However, the low potential and insufficiently high specific capacity lead to lower energy density, so it becomes imperative to find new cathodes with high potential and high specific capacity. Herein, a novel ternary lithium-rich Li₄Fe_0.5Mn_0.5V(PO₄)₃ (FMV) cathode is designed, which combines the high specific capacity of V, high potential of Mn and high stability of Fe. Multiple electron transfer by activation of multiple redox pairs of Fe²⁺/Fe³⁺, Mn²⁺/Mn³⁺, and V³⁺/V⁴⁺/V⁵⁺ at 2.0–4.5 V, demonstrated through the XPS results. The obtained Li₄Fe_0.5Mn_0.5V(PO₄)₃/C cathode, charging/discharging at 2.0–4.5 V, can deliver a specific capacity of ≈163.3 mAh g⁻¹ at 0.1C, and a capacity retention of 94.2% after 500 cycles at 5C. The reversibility and stability of the structure upon the charging/discharging process are revealed by ex-situ XRD. In addition, the redox reaction of V²⁺/V³⁺ can be activated by charging/discharging within 1.5–4.5 V, proving through the XPS of the electrodes at 2.0 and 1.5 V, so that it can deliver an amazing reversible specific capacity of ≈220 mAh g⁻¹ at 0.1 C, with a capacity retention of 91.1% after 200 cycles at 1C (≈170 mAh g⁻¹), providing new perspectives for high-performance Li-ion batteries.