Trace Y Doping Regulated Bulk/Interfacial Reactions of P2-Layered Oxides for Ultrahigh-Rate Sodium-Ion Batteries.

Abstract

P2-phase layered cathodes play a pivotal role in sodium-ion batteries due to their efficient Na+ intercalation chemistry. However, limited by crystal disintegration and interfacial instability, bulk and interfacial failure plague their electrochemical performance. To address these challenges, a structural enhancement combined with surface modification is achieved through trace Y doping. Based on a synergistic combination of experimental results and density functional theory (DFT) calculations, the introduction of partial Y ions at the Na site (2d) acts as a stabilizing pillar, mitigating the electrostatic repulsions between adjacent TMO2 slabs and thereby relieving internal structural stress. Furthermore, the presence of Y effectively optimizes the Ni 3d-O 2p hybridization, resulting in enhanced electronic conductivity and a notable rapid charging ability, with a capacity of 77.3mA h g-1 at 40C. Concurrently, the introduction of Y also induces the formation of perovskite nano-islands, which serve to minimize side reactions and modulate interfacial diffusion. As a result, the refined P2-Na0.65 Y0.025 [Ni0.33 Mn0.67 ]O2 cathode material exhibits an exceptionally low volume variation (≈1.99%), an impressive capacity retention of 83.3% even at -40°C after1500 cycles at 1C.