In–situ construction of LixFeyOz coatings on cobalt–free lithium–rich cathode materials for enhanced structural stability and electrochemical performance

Abstract

Environmentally benign and cost–effective cobalt–free lithium–rich cathode materials have garnered significant interest. Nevertheless, the irreversible loss of lattice oxygen compromises their structural integrity, leading to capacity fade, voltage decay, and sluggish kinetics, which collectively impede their commercial viability. To address these challenges, this study introduces an in–situ formation of Li_xFe_yO_z coatings on the surface of cobalt–free lithium–rich materials by utilizing residual lithium compounds. At elevated temperatures, the residual lithium compounds on the surface of Li_1.2Mn_0.6Ni_0.2O₂ (LMNO) react with FeO to generate a Li_xFe_yO_z protective layer. This coating not only shields the bulk material from direct exposure to the electrolyte but also effectively consumes residual lithium compounds to suppress interfacial side reactions, thereby enhancing structural stability. The Li_xFe_yO_z layer acts as a lithium–ion conductor, facilitating the migration of lithium ions and markedly boosting the material's electrochemical performance. Experimental results indicate that at a current density of 1C, the initial discharge specific capacity of LMNO@Fe is 235.24 mAh g⁻¹ with a capacity retention of 91.33 % after 100 cycles, compared to 211.62 mAh g⁻¹ and 77.95 % for LMNO, respectively. Even at a higher current density of 5C, the LMNO@Fe maintains a discharge specific capacity of 148.30 mAh g⁻¹. This research demonstrates that the Li_xFe_yO_z coating on cobalt–free lithium–rich cathode materials offers a promising strategy for achieving high–performance lithium–ion batteries.