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, O 2 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 W 6+ ions (0.75 ​at.%) can occupy T Li sites in Li 1 · 2 Mn 0·6 Ni 0·2 O 2 . T Li -site doping maximizes dopant efficiency, as each single W 6+ 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, O 2 release and formation of low-voltage Mn 3+ /Mn 4+ redox couple are inhibited, resulting in negligible voltage decay. • W 6+ doping at tetrahedral sites is visualized at the atomic scale. • Cation ordering in 0.75 ​at.% W 6+ -doped Li-rich cathode is maintained over 250 cycles. • The long-range Coulomb repulsion of W 6+ ions enables trace doping to exert a broad stabilizing effect. • 0.75 ​at.% W 6+ -doped Li-rich cathode exhibits negligible voltage decay.

Topics & Concepts