Fe3+ and PO4 3- co-doped Li-rich Li1.20Mn0.56Ni0.16Co0.08O2 as cathode with outstanding structural stability for Lithium-ion battery

Highlights: • Fe³⁺ and PO₄^3- are successfully co-doped into Li_1.20Mn_0.56Ni_0.16Co_0.08O₂ via a novel wet chemical method. • The co-doping constructs a stable layered structure. • The introduced dual ions improve the reversible specific capacity and high rate performance. • The synergistic effects of Fe³⁺ and PO₄^3- effectively inhibit the structural transformation and mitigate the voltage decay. -- Abstract: The Li-rich Mn-based cathode materials exhibit great potential due to their ultrahigh specific capacity, but still suffer from low initial coulombic efficiency, inferior cycling stability, voltage decay and poor rate performance. In this study, we propose to enhance the structural stability and the electrochemical performances of Li_1.20Mn_0.56Ni_0.16Co_0.08O₂ through the co-doping of Fe³⁺ and PO₄^3-. The Fe³⁺ and PO₄^3- are simultaneously doped in the precursor via a novel wet chemical method. In comparison with the undoped or mono-doped samples, the co-doped sample exhibits the best electrochemical performances owing to the synergistic effect of Fe³⁺ and PO₄^3-, such as a high initial coulombic efficiency (88%), great cyclic stability (remains a specific capacity of 214 mAh g⁻¹ after 130 cycles at 1 C) and mitigated voltage fade (2.12 mV per cycle). The synergistic mechanism of Fe³⁺ and PO₄^3- is revealed based on X-ray diffraction, transmission electron microscope, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements. The co-doping of Fe³⁺ and PO₄^3- constructs a stable oxygen-packed framework, which can alleviate lattice distortion, reduce the mixing of cations and increase the reversible reaction of 2 O^2-/(O₂)^n-, contributing to outstanding structural stability. The synergetic strategy of anion and cation and the co-doping method in this work may provide some inspiration for designing the high-performance cathode materials of Lithium-ion battery.