Exploring the effects of lithium excess on LiNi_0.8Mn_0.1Co_0.1O₂ prepared from a commercial Ni_0.8Mn_0.1Co_0.1(OH)₂ precursor

Abstract

Optimizing the electrochemical performance of nickel-rich cathode materials, specifically Ni0.8Mn0.1Co0.1(OH)2 (NMC811) precursors, involves careful adjustment of several factors, including modification, calcination temperature and lithium content. In this study, we explored the influence of lithium content on the structural, morphological and electro­chemical performances of LixNi0.8Co0.1Mn0.1O2, by varying 5, 10, 15 and 20 mol.% of Li excess. An appropriate amount of Li was found to suppress cation mixing effectively. Rietveld refinement showed that increasing Li content gradually reduced cation mixing by enhancing the occupancy of Li⁺ ions at the 3a sites, thereby hindering Ni²⁺ migration. Although a higher Li addition (20 mol.%) induced a slight lattice contraction, it exhibited the highest c/a ratio (the ratio of the lattice parameters c and a in the layered hexagonal structure), indicative of a well-ordered layered structure. Furthermore, Li exceeded 20 mol.% suppressed the H2/H3 phase transition, contributing to greater structural stability during cycling. While 15 mol.% Li excess achieved the highest initial discharge capacity (185.42 mAh g-1 at 0.1 C), 20 mol.% Li excess exhibited superior capacity retention (82.05 % over 80 cycles at 0.1 C). These results demonstrate the critical role of lithium stoichiometry in maintaining structural integrity and electrochemical stability of Ni-rich NMC cathodes, offering valuable insights for the design of high-performance lithium-ion batteries.