Constructing Perovskite Phase to Enhance the Electrochemical Performance of a Cobalt-Free, Ultrahigh-Ni Cathode.

Abstract

Developing cobalt-free, ultrahigh-Ni cathode materials holds great significance for the sustainable advancement of lithium-ion batteries. However, ultrahigh-Ni cathodes without cobalt often suffer from severe Li⁺/Ni²⁺ mixing, which leads to poor Li⁺ diffusion kinetics and structural instability. Although the introduction of high-valent Mo⁶⁺ into the cobalt-free layered structure has been considered an effective strategy to optimize Li⁺ diffusion channels and dissipate the intergranular strain, it still cannot thoroughly resolve the anisotropic strain within the lattice. Herein, a distinctive in situ strategy is adopted to introduce La³⁺ into the precursor during the coprecipitation process; the perovskite phase (La₄(LiMn)O₈) is grown coherently within the layered lattice of LiNi_0.9Mn_0.08Mo_0.02O₂ (NMM) during the subsequent lithiation process. Structurally stable La₄(LiMn)O₈ significantly restrains the Li⁺/Ni²⁺ mixing, enlarges the Li-O interlayer spacing, and mitigates the intrinsic lattice strain by alleviating the H2 → H3 hexagonal phase transition. Thanks to these comprehensive structural advantages, the as-fabricated La-NMM cathode with the La₄(LiMn)O₈ demonstrates a reversible specific capacity of 176 mA h g^-1 at 5 C and retains 90% capacity after 100 cycles at 0.5 C. This in situ strategy broadens the prospects of phase engineering and provides design ideas for the development of practical cobalt-free, ultrahigh-Ni cathode materials.