A multifunctional dual cation doping strategy to stabilize high-voltage medium-nickel low-cobalt lithium layered oxide cathode

Abstract

High-voltage medium-nickel low-cobalt lithium layered oxide cathode materials are intriguing for lithium-ion batteries (LIBs) applications because of their relatively low cost and high capacity. Unfortunately, high charging voltage induces bulk layered structure decline and interface environment deterioration, low cobalt content reduces lithium diffusion kinetics, severely limiting the performance liberation of this kind of cathode. Here, a multifunctional Al/Zr dual cation doping strategy is employed to enhance the electrochemical performance of LiNi_0.6Co_0.05Mn_0.35O₂ (NCM) cathode at a high charging cut-off voltage of 4.5 V. On the one hand, Al/Zr co-doping weakens the Li⁺/Ni²⁺ mixing through magnetic interactions due to the inexistence of unpaired electrons for Al³⁺ and Zr⁴⁺, thereby increasing the lithium diffusion rate and suppressing the harmful coexistence of H1 and H2 phases. On the other hand, they enhance the lattice oxygen framework stability due to strong Al-O and Zr-O bonds, inhibiting the undesired H2 to H3 phase transition and interface lattice oxygen loss, thereby enhancing the stability of the bulk structure and cathode-electrolyte interface. As a result, Al/Zr co-doped NCM (NCMAZ) shows a 94.2 % capacity retention rate after 100 cycles, while that of NCM is only 79.4 %. NCMAZ also exhibits better rate performance than NCM, with output capacities of 92 mAh/g and 59 mAh/g at a high current density of 5C, respectively. The modification strategy will make the high-voltage medium-nickel low-cobalt cathode closer to practical applications.

Keywords: Dual cation doping; High-voltage low-cobalt cathode; Lattice oxygen stability; Li(+)/Ni(2+) mixing; Lithium-ion battery.