Screening high-entropy dopants to modulate microstructure of high-nickel layer cathodes for overcoming fast Li+ kinetics-stable structure trade-off

Abstract

The intrinsic structural instability brings challenge for the high-nickel layered oxide cathode to break the trade-off between high rate capacity and cycle stability. Here, we screen out four doping elements (Al, Mg, Zr, Zn) based on the formation energy, and successfully synthesize a novel high-entropy cathode of LiNi_0.8Mn_0.1Co_0.02Cr_0.02Mg_0.02Zn_0.02Al_0.02O₂ (HEOCMZA). Due to the Ni-site substitution of multi-dopants, HEOCMZA achieves the highest configurational entropy, ensuring structural stability during the long-term cycling. In-situ characterizations and theoretical calculations furtherly verify that the high-entropy doping tailors the lattice structure, which radially stretches the Li unit cell while compresses the Ni unit cell, thereby enlarging the Li⁺ diffusion channel in the Li layer and increasing the Ni²⁺ migration energy barriers in the transition metal (TM) layer. Therefore, the high-entropy-triggered lattice distortion effect and sluggish diffusion effect not only accelerate Li⁺ diffusion but also suppress phase transition. In addition, the cocktail effect of high-entropy dopants increases the area of “Fermi Sea”, enhancing the electronic conductivity, as well as pins the TM-O, mitigating the O₂ release and microcracks. Consequently, benefitted from the synchronous enhancements of the structural strength and Li⁺ diffusion kinetics, the HEOCMZA battery exhibits a remarkable cycle stability (remaining 85.88 % after 200 cycles at 1 C), the distinguished rate capability (10 C, 136.7 mAh g⁻¹), especially the superior capacity retention (77.03 %, 100 cycles) at 10 C, outperformed other doped counterparts reported to date. This proposed strategy of applying high-entropy effects to modulate the microstructure provides an insightful guidance in the design of high-energy-density battery materials.