Single‐Crystal LiNi<i>_x</i>Mn<i>_y</i>Co₁₋<i>_x</i>₋<i>_y</i>O₂ Cathodes for Extreme Fast Charging

Abstract

Ni-rich layered LiNi_x Mn_y Co_1- _x _- _y O₂ (NMCs, x ≥ 0.8) are poised to be the dominating cathode materials for lithium-ion batteries for the foreseeable future. Conventional polycrystalline NMCs, however, suffer from severe cracking along the grain boundaries of primary particles and capacity loss under high charge and/or discharge rates, hindering their implementation in fast-charging electric vehicular (EV) batteries. Single-crystal (SC) NMCs are attractive alternatives as they eliminate intergranular cracking and allow for grain-level surface optimization for fast Li transport. In the present study, the authors report synthetic approaches to produce SC LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NMC811) samples with different morphologies: Oct-SC811 with predominating (012)-family surface and Poly-SC811 with predominating (104)-family surface. Poly-SC811, representing the first experimentally synthesized NMC811 single crystals with (104) surface, delivers superior performance even at the ultra-high rate of 6 C. Through detailed X-ray analysis and electron microscopy characterization, it is shown that the enhanced performance originates from better chemical and structural stabilities, faster Li⁺ diffusion kinetics, suppressed side reactions with electrolyte, and excellent cracking resistance. These insights provide important design guidelines in the future development of fast-charging NMC-type cathode materials.