Correlation between Manganese Dissolution and Dynamic Phase Stability in Spinel-Based Lithium-Ion Battery

Abstract

Historically long accepted to be the singular root cause of capacity fade, transition metal dissolution and its subsequent anode deposition have been reported to interfere with Li intercalation and destroy the anode solid electrolyte interphase. However, as a vital battery component, cathode behavior under transition metal dissolution still remains unclear. Here we report an unequivocal relationship between capacity fade and both dynamic phase stability and surface chemical stability of the cathode. With spinel LiMn2O4 as a model system and a Li-rich LiMn2O4 control sample, clear evidence gathered through in-situ/ex-situ high energy X-ray diffraction and scanning transmission electron microscopy reveal, for the first time, that a combination of dynamic structural transformation and surficial transition metal dissolution are the dominant factors of cathode capacity fade. LiMn2O4 exhibits irreversible phase transitions driven by Mn(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks formed during repeated charge/discharge result in severe Mn dissolution. Meanwhile, fast Mn dissolution in turn triggers irreversible structural evolution. These two processes form a detrimental chemical-cycle that constantly consumes the capacity of spinel. Furthermore, we are able to reproduce the atomic structural advantages of Li-rich LiMn2O4 with Li/Mn disorder and surface reconstruction, effectively suppressing the irreversible phase transition and Mn dissolution. These findings, predominately caused by transition metal dissolution and a newly discovered irreversible phase transition, close the loop of understanding capacity fade mechanisms in spinel-based cells. This insight helps elucidate structure stability improvements found from Li enrichment and cation doped cathodes, allowing for development of longer life batteries.