A Cobalt‐Free Li(Li_0.17Ni_0.17Fe_0.17Mn_0.49)O₂ Cathode with More Oxygen‐Involving Charge Compensation for Lithium‐Ion Batteries

Abstract

High-energy-density and low-cost lithium-ion batteries are sought to meet increasing demand for portable electronics. In this study, a cobalt-free Li(Li_0.17 Ni_0.17 Fe_0.17 Mn_0.49 )O₂ (LNFMO) cathode material is chosen, owing to the reversible anionic redox couple O^2- /O^- . The aim is to elucidate the Fe-substitution function and oxygen redox mechanism of experimentally synthesized Li(Li_0.16 Ni_0.19 Fe_0.18 Mn_0.46 )O₂ by DFT. The redox processes of cobalt-containing Li(Li_0.17 Ni_0.17 Co_0.17 Mn_0.49 )O₂ (LNCMO) are compared with those of LNFMO. Redox couples including Ni²⁺ /Ni³⁺ /Ni⁴⁺ , Fe³⁺ /Fe⁴⁺ or Co³⁺ /Co⁴⁺ , and O^2- /O^- are found, confirmed by a X-ray photoelectron spectroscopy, and explained by redox competition between O and transition metals. In LNFMO and LNCMO, O ions with an Li-O-Li configuration readily participate in oxidation, and the most active O ions are coordinated to Mn⁴⁺ and Li⁺ . Oxidation of O in LNCMO is triggered earlier, along with that of Co. Fe substitution activates O ions, contributes additional oxygen redox charge compensation of 0.44 e per formula unit, avoids concentrated accumulation of oxygen oxidation, and improves structural stability. This work provides new scope for designing cobalt-free, low-cost, and higher-energy-density cathode materials for Li-ion batteries.