Dual-functional vanadium doping for enhanced structural stability and Li+ transport in Co-free Li-rich Mn-based Li1.2Ni0.2Mn0.6O2 cathodes

초록

Cobalt-free Li-rich Mn-based (LRNM) cathodes are promising next-generation materials with notable cost competitiveness and reversible capacities >250 mAh g(-1). However, their practical application remains limited because of irreversible lattice O release and severe voltage decay accompanied by spinel/rock-salt phase transitions and structural degradation. V-doped LRNM (Li1.2Ni0.2-x/2Mn0.6-x/2VxO2, x = 0.02, 0.04, 0.06) is synthesized in this study via a hydrothermal process followed by a solid-state reaction. An appropriate amount of V doping enables a dual stabilization mechanism, namely, lattice O stabilization through the formation of strong V-O bonds and interfacial stabilization via a thin rock-salt protective layer formed on the surface. Furthermore, the V5+ doping-induced charge compensation effect (Ni3+/Mn4+ -> Ni2+/Mn3+) results in lattice expansion along the c-axis, thereby widening the Li+ diffusion channels and enhancing ionic conductivity. Consequently, the optimized composition, V4-LRNM, exhibits a reduced irreversible capacity loss (28 mAh g(-1)) caused by O release, a 10% capacity retention improvement after 100 cycles at 1 C, and effectively suppressed voltage decay (Delta V = 0.22 V). This study demonstrates that V doping is a viable strategy for simultaneous lattice and interfacial stabilization, offering an effective pathway for the practical implementation of LRNM cathodes.

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