In-situ conversion of residual alkali into fast-ion conductor coating and synchronously realizing gradient Mo4+ doping to stabilize LiNi0.9Mn0.1O2 cathode.

The surficial residual alkali is a key factor that leads to aggravated phase transition and decay in cobalt-free high-nickel cathode. In this paper, we develop a one-step in-situ modification technique to convert the residual alkali on the LiNi 0.9 Mn 0.1 O 2 (NM91) surface into Li 2 MoO 4 coating. As a fast ionic conductor, Li 2 MoO 4 coating not only facilitate Li+ diffusion, but also inhibits the transition from layered to rock salt phase on the cathode surface. Moreover, the multi-aperture architecture formed in the conversion promotes the high-valent Mo enter-into the lattice and realizes the gradient doping of Mo4+ through thermodynamic diffusion. Due to the pillar effect, Mo doping increases c-axis spacing, mitigates cation mixing, and reduces the irreversible H2-H3 phase transition. As a result, both the Li+ diffusion kinetics and thermodynamic stability are improved. Consequently, the as-prepared Mo modified NM91 exhibits an increased capacity retention from original 62.3–75.6 % (100 cycles, 0.2 C) and enhanced rate capability of 131.96 mAh g−1 at 5.0 C. This work provides a facile "reducing alkali" technological process, and lays foundation for the material design and performance optimization of high energy density cathodes in lithium-ion batteries. • Cobalt-free high nickel LiNi 0.9 Mn 0.1 O 2 cathode material was synthesized, and LiNi 0.9 Mn 0.1 O 2 was modified by doping and coating synergistically by one-step method to achieve a discharge capacity of 131.91 mAh g−1 at 5 C rate (LiNi 0.9 Mn 0.1 O 2 is only 77.7 mAh g−1) and a capacity retention rate of up to 75.6 % after 100 cycles at 0.2 C (LiNi 0.9 Mn 0.1 O 2 is only 62.3 %). • The mechanism of synergistic modification on the interfacial side reaction and structural stability of cobalt-free high nickel materials was clarified by characterization and DFT calculation. • The help of in-situ alkali reduction process to improve the stability of cobalt-free high nickel cathode materials was studied in a pioneering way, which laid a foundation for the correlation of interface stability and performance optimization of cobalt-free high nickel cathode materials, and had potential industrial application prospects. [ABSTRACT FROM AUTHOR]