Li-rich layered oxides (LLOs) are considered as the cathode materials for the next generation of lithium-ion batteries because of their high specific capacity. However, due to the structural rearrangement in the charging and discharging process, the initial Coulombic efficiency (ICE) is low and accompanied by serious voltage attenuation and bad cycle performance. In this work, the Li-gradient layer on the surface of the rod-like LLOs is constructed by the treatment of (NH 4 ) 2 SiF 6 under high temperature and subsequent washing. XRD, HRTEM, and Raman spectra verify the existence of the spinel phase of Li 1−x Mn 2 O 4 on the surface of LLOs by the modification. The results of electrochemical measurements show that the modified LLOs exhibit a higher ICE of 87% with an excellent cycling retention of 90.4% (after 100 cycles at 1 C). These improvements on the electrochemical performance are caused by the high Li + diffusion and improved the redox reversibility of oxygen ions on the LLOs with the unique structure of the Ligradient and spinel coating layer on the surface.

As a result of the redox reaction of lattice oxygen occurring at 4.5 V, the Li-rich manganese cathode material with an O3 configuration has a theoretically high discharge capacity (>250 mA h/g). However, it also suffers a structural transition from layered structure to spinel structure in the cycling process, leading to severe voltage decay and capacity fading. On contrary, the O6 type material obtained via ion exchange of P2 type material can effectively inhibit the phase transition and stabilize the layered structure. Hence, in this work, we design an O6/O3 multi-phase composite material after ion exchange of the P2/O3 nanocrystalline composite. Compared with the O3 type cathode, the as-obtained cathode composite exhibits a higher initial discharge capacity (≈265 mA h/g at 20 mA/g) and an excellent capacity retention (≈87% after 100 cycles). Moreover, the first cycle Coulombic efficiency increases by nearly 10%, and voltage attenuation is effectively inhibited. Our findings demonstrate that modulating the O6/O3 configuration is a practical and simple methodology to promote the electrochemical performance of lithium-rich layered materials.

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