Sanghoon Choy

Impacts of Surface Mn Valence on Cycling Performance and Surface Chemistry of Li- and Al-Substituted Spinel Battery Cathodes

The Mn 4+ -abundant surface of the Li- and Al-substituted spinel cathode materials is found to provide electrochemical and interfacial stabilities in the voltage region of 3.3-4.3 V vs. Li/Li + in the room temperature electrolyte of 1M LiPF 6 /EC:DEC. Surface characterization using ex situ X-ray photoelectron spectroscopy reveals that surface Mn 4+ -abundance induces the formation of a plenty of new surface components and the passivation of cathode surface before being reduced to Mn 3+ to Mn 2+ , leading to capacity retention 90% with discharge capacities 102-90 mAh/g over 50 cycles. FTIR spectroscopic analysis results and scanning electron microscopic imaging ensure that the Mn 4+ -abundant surface is better passivated by solid electrolyte interphase (SEI) layer that is composed of mixed organic and inorganic compounds, resulting in somewhat preserved particle morphology. On the contrary, the cathodes with equal amounted surface Mn 4+ /Mn 3+ and Mn 3+ -abundant surface are readily subjected to severe interfacial reaction and particle morphology change accompanied by inferior surface coverage by surface species, which are responsible for a rapid capacity fade. The data contribute to a basic understanding of importance of surface control and its impact on the cycling performance of spinel-based cathode materials for lithium-ion batteries.