Advances in mitigating oxygen evolution, phase transformation, and voltage fading in Li/Mn-rich cathode materials via cationic doping and surface modification

Abstract

The Li/Mn-Rich Li[Li x TM (1- x ) ]O 2 (0 < x ≤ 0.2, transitional metals (TMs) = Ni, Mn, & Co) cathode materials are practical alternatives to the dominant lithium iron phosphate (LFP), nickel‑cobalt‑aluminum (NCA), and Ni-rich NMCs owing to their high practical discharge capacities of ∼250–350 mAh/g at elevated voltages (>4.5 V). However, the Li/Mn-rich chemistry commercialization has been impeded by oxygen (O 2 ) evolution, layered to spinel phase transformation, voltage fading, and electrolyte decomposition during cycling. The activation of the Li 2 MnO 3 component is associated with the irreversible first cycle capacity loss of up to 100 mAh/g. On a positive note, spinel phase formation, O 2 evolution, and voltage fading can be mitigated by cationic doping, surface and electrolyte modification. Doping with Na, Nb, K, and Sn expands the Li-slab space and the a / c lattice parameters for better Li + diffusion while cationic dopants stabilize the TM–O bond, occupy the tetrahedral sites in the TM layer, preventing the formation of tri-vacancies and spinel phases; this enhances the cycling stability and suppresses voltage fading. Surface modification with metal oxides (such as TiO 2 and Y 2 O 3 ), phosphates (Li 3 PO 4 /CePO 4 ) and Li–salts (LiAlF 4 ) mitigate oxygen evolution and HF attack, while electrolyte modification improved the stability of the electrolyte at higher voltages suppressed electrolyte decomposition and contributed to the formation of a stable cathode electrolyte interface. • The synergistic beneficial effects of cationic doping, surface coating, and electrolyte modification are discussed. • Cationic dopants and phosphates/metal oxides/Li-salts-based coatings increase the energy barrier for O 2 evolution. • Cationic dopants and phosphates/metal oxides/Li-salts coating suppress layered to spinel phase formation and voltage decay. • Cationic doping, surface modification, electrolyte modification addresses barriers to commercializing Li/Mn-rich cathodes.