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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]

Closely wrapped Si@graphene structure with improved contacting interface were synthesized by a facile compression method. The improved contacting interface have greatly enhanced the positive effect of graphene sheets on restraining the volume change of Si nanoparticles and improving the electronic conductivity. The obtained composite sample shows significantly improved electrochemical performance as anode material for Li-ion batteries. [Display omitted] • Closely wrapped Si@graphene structure with improved contact interface was synthesized by a facile compression method. • The improved contact interface has enhanced the effect of graphene on restraining the volume change of Si nanoparticles. • The composite sample shows significantly improved cycling stability and rate performance. Despite their extremely high capacity (4200 mA h g−1), the practical application of silicon anodes is still frustrated by their poor cycling performance, resulting from severe volume changes and pulverization of the electrode material. Introducing graphene in silicon is an ideal approach for addressing these issues. Nevertheless, the large size difference between Si and graphene makes high-quality contact difficult to realize, which severely harms the electrochemical performance of Si/graphene composites. Herein, a unique Si@graphene layer structure (p-Si@GN) with an improved contact interface is fabricated by a facile high-pressure method, in which the surfaces of silicon particles are closely covered by graphene layers, restraining the volume changes from multiple angles. The superior structure of the layered p-Si@GN composite exhibits multiple desired features for high-performance Si-based anodes, such as high Li+ storage capacity resulting from high-capacity Si nanoparticles, outstanding electron conductivity due to the formation of a continuous graphene conductive network, and excellent structural stability due to the enhanced protective function of graphene layers with an improved contact interface. Due to these advantages, the p-Si@GN 40 anode, prepared under 40 MPa pressure, exhibits a significantly improved capacity of 2096.9 mA h g−1 at a current density of 300 mA g−1, an enhanced rate capability of 706.4 mA h g−1 at 3000 mA g−1, and superior cycling performance with a high capacity retention of 82.6 % after 150 cycles. [ABSTRACT FROM AUTHOR]