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[Display omitted] Benefiting from the extra contribution of O redox, Co-free Li-rich layered oxides (LRNMO) can satisfy the requirement of high specific capacities. However, during the high-voltage charging process, lattice oxygen being oxidized to O− or O 2 leads to a gradual transition of the structure from layered to spinel phase, capacity and voltage decline, hindering the practical application of LRNMO in the lithium-ion battery. Here, a surface modification strategy of Li 1.2 Ni 0.32 Mn 0.48 O 2-δ doped with Ta5+ ions is proposed, in which the Ta5+ ions occupy the lithium sites of the lattice structure on the surface layer of LRNMO and form a Ta 2 O 5 coating layer. The modified electrode exhibits excellent rate performance and cycling stability, with 94.9% and 85.5% capacity retention rate and voltage retention rate, respectively, after 200 cycles at 1C. Moreover, the initial coulomb efficiency and ionic conductivity of the modified electrode are also apparently enhanced. Simultaneously, the decreased Li/Ni mixing degree of the modified electrode reflects the improvement of the structural stability. Therefore, the modification strategy through strong metal–oxygen bonding to integrate the surface structure to regulate the oxygen activity provides a new direction for the design of high energy density Co-free Li-rich cathode materials. [ABSTRACT FROM AUTHOR]

[Display omitted] Benefiting from the extra contribution of O redox, Co-free Li-rich layered oxides (LRNMO) can satisfy the requirement of high specific capacities. However, during the high-voltage charging process, lattice oxygen being oxidized to O− or O 2 leads to a gradual transition of the structure from layered to spinel phase, capacity and voltage decline, hindering the practical application of LRNMO in the lithium-ion battery. Here, a surface modification strategy of Li 1.2 Ni 0.32 Mn 0.48 O 2-δ doped with Ta5+ ions is proposed, in which the Ta5+ ions occupy the lithium sites of the lattice structure on the surface layer of LRNMO and form a Ta 2 O 5 coating layer. The modified electrode exhibits excellent rate performance and cycling stability, with 94.9% and 85.5% capacity retention rate and voltage retention rate, respectively, after 200 cycles at 1C. Moreover, the initial coulomb efficiency and ionic conductivity of the modified electrode are also apparently enhanced. Simultaneously, the decreased Li/Ni mixing degree of the modified electrode reflects the improvement of the structural stability. Therefore, the modification strategy through strong metal–oxygen bonding to integrate the surface structure to regulate the oxygen activity provides a new direction for the design of high energy density Co-free Li-rich cathode materials. [ABSTRACT FROM AUTHOR]

• Co-free lithium-rich material was prepared by simple oxalate co-precipitation way. • The nano-micron combined structure was favorable to the infiltration of electrolyte. • The anions regulated the valence of surface transition metal ions. • The F-doped electrode exhibited excellent cycle stability. Co-free cathode materials are gradually attracted wide attention due to the low budget and environmental friendliness, but their application is still prevented by the poor rate performance and cyclic stability. Herein, the Co-free lithium-rich cathode materials (Li 1.2 Ni 0.2 Mn 0.6 O 2 , LRNMO) with a nano-micron combined morphology is prepared by a simple oxalate co-precipitation route and further modified by an anion doping strategy. It has been found that the F− anion doping can increase the content of Mn4+ in LRNMO, reduce the influence of the Jahn-Teller effect, and further impede the transition from layered phase to spinel phase. As a result, the as-obtained Li 1.2 Ni 0.2 Mn 0.6 O 2-x F x (x = 0.04, named as F4-LRNMO) shows an optimal electrochemical performance, for instance, high discharge capacity (243 mAh g−1) with a satisfactory initial coulombic efficiency of 84.37% at 0.1C. Meanwhile, the F4-LRNMO sample also can display high capacity retention of 92.2% after 200 cycles at 1C, and a remarkably high discharge capacity of 151 mAh g−1 with capacity retention of 95.4% after 100 cycles even at high rate of 5C. In consequence, this work can not only ameliorate the defects of poor stability and low initial coulomb efficiency, but also offer a meaningful exploration for the development of Co-free lithium-rich cathode materials with high capacity and high performance-price ratio. [ABSTRACT FROM AUTHOR]