Single-dopant long-range stabilization in long-cycled Li-rich layered cathodes via trace tetrahedral-site doping

Abstract

Migration of transition metal (TM) ions out of the TM layer is detrimental and unavoidable in lithium-rich layered oxides, which drives in-plane cation migration, O₂ release and energy loss. Since out-of-plane migration generally occurs through tetrahedral interstices (T_Li) in the Li layer, doping T_Li sites has been believed as a promising way to block migration pathways at the dopant site. However, with only trace dopants (<1 ​at.%) sparsely distributed in bulk, the ability of isolated dopants to suppress cation disorder in undoped regions remains unknown—largely due to no suitable model materials. Here, combining atomic-scale imaging, X-ray diffraction measurements and first-principles calculations, we demonstrate that W⁶⁺ ions (0.75 ​at.%) can occupy T_Li sites in Li_1·2Mn_0·6Ni_0·2O₂. T_Li-site doping maximizes dopant efficiency, as each single W⁶⁺ ion exerts a long-range Coulomb repulsion on TM/Li⁺ ions in the TM layer, suppressing both in-plane and out-of-plane cation migration over a broad range (∼2 ​nm diameter), in contrast to local stabilization via other doping techniques. Remarkably, cation ordering is preserved for over 250 cycles, far exceeding the limited structural stability (∼50 cycles) typically achieved with conventional modification strategies. Consequently, O₂ release and formation of low-voltage Mn³⁺/Mn⁴⁺ redox couple are inhibited, resulting in negligible voltage decay.