Abstract:

Spinel LiMn₂O₄ cathode is widely used in aqueous lithium-ion batteries whose electrochemical performance are highly dependent on its material properties including the chemical composition, particle size, morphology, crystal structure and so on. In this study, we objectively investigate three typical kinds of spinel LiMn₂O₄: pure LiMn₂O₄, LiAl _x Mn_{2- x} O₄, and Li_{1+ x} Mn_{2- x} O₄ respectively in super-high concentrated aqueous electrolytes. The evolution of crystal structure, morphology and chemical composition with the cycles carefully investigate by a series of chemical analysis (ICP), crystal structure (XRD), morphology characterization (TEM, SEM) and multiple electrochemical methods (EIS, CV) whose influence on the electrochemical performances is discussed detailly. It is discovered that pure LiMn₂O₄ is prone to Mn dissolution and Jahn-teller distortion resulting in the irreversible phase transitions and structure detraction thereby leading to severe capacity fading; the trace amount of Al³⁺ doping in LiMn₂O₄ enables to suppress the Jahn-Teller effect of Mn to a certain extent but cannot avoid completely Mn dissolution and lattice deformation whose cycling fading still exists evidently; compared with above-mentioned two kinds of cathodes, lithium-rich Li_{1+ x} Mn_{2- x} O₄ presents much better electrochemical performance because the introduction of excessive Li in the crystal structure is favorable to effectively inhibit Mn dissolution and suppress Jahn-Teller distortion, thereby, it is suggested as an ideal cathode candidate for aqueous lithium ion battery.

Key words: spinel LiMn₂O₄, Al³⁺ doping, lithium-rich, Jahn-Teller distortion, electrochemical performance