The high capacity of Li‐rich and Mn‐based (LRM) cathode materials is originally due to the unique hybrid anion‐ and cation redox, which also induces detrimental oxygen escape. Furthermore, the counter diffusion of released oxygen (into electrolyte) and induced oxygen vacancies (into the interior bulk phase) that occurs at the interface will cause uncontrolled phase collapse and other issues. Therefore, due to its higher working voltage (>4.7 V) than the activation voltage of lattice oxygen in LRM (≈4.5 V), the anion‐redox‐free and structurally consistent cobalt‐free LiNi0.5Mn1.5O4 (LNMO) is selected to in situ construct a robust, crystal‐dense and lattice‐matched oxygen‐passivation‐layer (OPL) on the surface of LRM particles by the electrochemical delithiation to protect the core layered components. As expected, the modified sample displays continuously decreasing interfacial impedance and high specific capacity of 135.5 mAh g‐1 with a very small voltage decay of 0.67 mV per cycle after 1000 cycles at 2 C rate. Moreover, the stress accumulation during cycling is mitigated effectively. This semicoherent OPL strengthens the surface stability and interrupts the counter diffusion of oxygen and oxygen vacancies in LRM cathode materials, which would provide guidance for designing high‐energy‐density layered cathode materials.
Li-rich layered oxides (LLOs) are supposed to be the most competitive cathode materials for lithium-ion batteries (LIBs), because of the high theoretical specific capacities (>250 mAh g −1 ). However, there are some inherent inferiorities, such as the low initial Coulombic efficiency (ICE) and the rapid capacity/voltage decay, that hinder the large-scale commercial applications of LLOs. Herein, we successfully obtained spinel-coated and phosphate-doped Co-free Li-rich layered oxides (Co-free LLOs) by cotreatment methods, using weakly acidic and alkalinity (NH 4 H 2 PO 4 solution), which could effectively improve the electrochemical performance. The spinel coating could not only accelerate the movement of Li + but also restrain O 2 release, while the doping PO 4 3− could inhibit the transition-metal (TM) migration between the oxygen octahedral site and the oxygen tetrahedral site. The optimized Co-free LLOs cathode treated with 3% NH 4 H 2 PO 4 solution could deliver a high ICE of 88% and a high discharge capacity up to 159.5 mAh g −1 after 500 cycles at 1C (1C = 250 mA g −1 ). Moreover, the voltage fading decreases from 0.64 mV to 0.32 mV per cycle during cycling. This work provides new insights for developing high-performance Co-free LLOs cathode materials.
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