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| Hauptseite > Publikationsdatenbank > Establishing an Appropriate Voltage Window for Stable Cycling of Li/Mn-Rich Layered Oxide || Graphite Full Cells |
| Hauptseite > Publikationsdatenbank > Establishing an Appropriate Voltage Window for Stable Cycling of Li/Mn-Rich Layered Oxide || Graphite Full Cells |
| Journal Article | FZJ-2024-02672 |
; ; ;
2023
Soc.
Pennington, NJ
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Please use a persistent id in citations: doi:10.1149/MA2023-012665mtgabs
Abstract: Li/Mn-rich layered oxide cathode active materials (LMR) have gained attention due to their exceptionally high practical specific discharge capacity (>250 mAh g-1) originating from both conventional cationic as well as anionic oxygen redox contributions. To achieve this high capacity, the Li2MnO3-like regions of the material, which give rise to oxygen redox need to be electrochemically activated at high voltage (above 4.6 V versus Li+/Li0). This high voltage activation, however, results in the destabilization of lattice oxygen that creates subsequent adverse phenomena such as first-cycle hysteresis and the evolution of redox couples. The latter happens continuously during cycling and results in the activation of Mn3+/Mn4+ redox couple. This redox couple involving Mn3+ is problematic because, at this oxidation state, Mn disproportionation reaction can occur, resulting in the formation of highly soluble Mn2+ species. In a half-cell setup, the impact of Mn dissolution may be subtle, however, in LMR||Graphite full cells, the impact is consequential.This work focuses on investigating the degradation mechanism of LMR||Graphite full cells at different voltage windows applied during the activation cycles and the long-term cycling. These different voltage windows alter the redox contributions and thus affect the long-term performance of the cells. We observe that lowering the upper cut-off voltage (UCV) from 4.7 V to 4.5 V during the entire cycling process can increase capacity retention, although rapid degradation can still be observed. Only when the UCV during the long-term cycling is lowered to 4.3 V, can we obtain incremental degradation of the cells. We also show that lowering the activation cycles UCV to 4.5 V is beneficial for long-term cycling due to the lower contribution of Mn3+/Mn4+ redox couple after the activation cycles. Finally, we observe that increasing the lower cut-off voltage from 1.9 V to 2.4 V results in higher discharge voltage. Nevertheless it is followed by a reduction in discharge capacity, resulting in a lower specific energy. This study offers insights into the high-voltage cycling performance of practical LMR||Gr full cells that can be used for the foundation of material design to alleviate the adverse effect of oxygen redox in LMR.
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