Surface energy alteration-derived grain size regulation countering capacity deterioration in high-voltage single-crystal Ni-rich cathodes

Abstract

Single-crystal Ni-rich cathodes possess prominent structural integrity and thermal stability compared to their poly-crystal counterparts, yet their application at high voltage is hampered by the intragranular cracks that remain intractable for mitigation. Herein, a novel niobium-modified single-crystal LiNi_0.83Co_0.12Mn_0.05O₂ (NCM) cathode, which integrates grain size and lattice regulation superiorities, is designed. The results demonstrate that doped Nb⁵⁺ reduces the surface energies of (001), (012), and (104) faces, followed by the diminution of critical nuclei size and grain size based on the classical nucleation theory. Smaller grain size effectively facilitates the release of internal strain, resulting in fewer planar slips and intragranular cracks inside the niobium-modified cathodes. Moreover, a heterogeneous surface structure derived by Nb⁵⁺ doping acts as a shield to alleviate the deleterious interfacial phase transition. Under a high-voltage of 4.4 V, the 0.5 mol% Nb⁵⁺-doped NCM displays an outstanding discharge capacity (211.3 mA h g⁻¹) at 0.1C, higher capacity retention (155.0 mA h g⁻¹vs. 130.2 mA h g⁻¹) at 1C after 100 cycles and a superior rate capacity (152.3 mA h g⁻¹vs. 118.9 mA h g⁻¹) at 5C in comparison with the pristine material. This bifunctional regulation strategy provides novel insights into the rational design of single-crystal Ni-rich cathodes.