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It has been a long-term challenge to improve the phase stability of Ni-rich LiNi x Mn y Co 1−x−y O 2 (x ≥ 0.6) transition metal (TM) oxides for large-scale applications. Herein, a new structure engineering strategy is utilized to optimize the structural arrangement of Li 1+x (Ni 0.88 Mn 0.06 Co 0.06 ) 1−x O 2 (NMC88) with a different Li-excess content. It was found that structure stability and particle sizes can be tuned with suitable Li-excess contents. NMC88 with an actual Li-excess of 2.7% (x = 0.027, Li/TM = 1.055) exhibits a high discharge capacity (209.1 mAh g −1 at 3.0−4.3 V, 0.1 C) and maintains 91.7% after the 100th cycle at 1 C compared with the NMC88 sample free of Li-excess. It also performs a delayed voltage decay and a good rate capacity, delivering 145.8 mAh g −1 at a high rate of 10 C. Multiscale characterization technologies including ex/in situ X-ray diffraction (XRD), focused ion beam (FIB) cutting-scanning electronic microscopy (SEM), and transmission electron microscopy (TEM) results show that a proper Liexcess (2.7%) content contributes to the formation of a broader Li slab, optimized cation mixing ratio, and even particle sizes. Therefore, NMC88 with a proper Li-excess is a good choice for next-generation cathode materials.

A Li-rich layered cathode material Li 1.2 Ni 0.2 Mn 0.6 O 2 with enhanced electrochemical performance has been fabricated by combining the Cr doping and LiAlO 2 coating. The structural characterization shows the perfect layered crystal structure. The 3 wt % LiAlO 2 -coated Li 1.2 Ni 0.16 Mn 0.56 Cr 0.08 O 2 shows the highest discharge specific capacity and the best cycling stability among different coating levels. The first discharge specific capacity is enhanced from 230.4 mAhg −1 to 268.8 mAhg −1 .The capacity retention ratio is improved from 92.7% to 97.3% after 100 cycles. The spinel phase is suppressed effectively in the 3 wt % LiAlO 2 -coated Li 1.2 Ni 0.16 Mn 0.56 Cr 0.08 O 2 . The midpoint voltage value of Li 1.2 Ni 0.2 Mn 0.6 O 2 after 100 cycles is enhanced from 2.746 to 3.128 V with Cr doping and LiAlO 2 coating. The lower R ct (charge transfer resistance) and higher D Li + (ion diffusion coefficient) of 3 wt % LiAlO 2 -coated Li 1.2 Ni 0.16 Mn 0.56 Cr 0.08 O 2 contribute to the excellent rate capability. The results suggest that ion doping combined with fast ion conductor coating is an effective way to enhance the electrochemical properties of the Li-rich layered cathode materials.