Improving the Structure and Cycling Stability of Ni-Rich Layered Cathodes by Dual Modification of Yttrium Doping and Surface Coating

Abstract

A crucial challenge for the commercialization of Ni-rich layered cathodes (LiNi_0.88Co_0.09Al_0.03O₂) is capacity decay during the cycling process, which originates from their interfacial instability and structural degradation. Herein, a one-step, dual-modified strategy is put forward to in situ synthesize the yttrium (Y)-doped and yttrium orthophosphate (YPO₄)-modified LiNi_0.88Co_0.09Al_0.03O₂ cathode material. It is confirmed that the YPO₄ coating layer as a good ion conductor can stabilize the solid-electrolyte interface, while the formative strong Y-O bond can bridle TM-O slabs to intensify the lattice structure in the state of deep delithium (>4.3 V). In particular, both the combined advantages effectively withstand the anisotropic strain generated upon the H2-H3 phase transition and further alleviate the crack generation in unit-cell dimensions, assuring a high-capacity delivery and fast Li⁺ diffusion kinetics. This dual-modified cathode shows advanced cycling stability (94.1% at 1C after 100 cycles in 2.7-4.3 V), even at a high cutoff voltage and high rate, and advanced rate capability (159.7 mAh g^-1 at 10C). Therefore, it provides a novel solution to achieve both high capacity and highly stable cyclability in Ni-rich cathode materials.