The Impact of Lithium Substitution on the Gassing Behavior and Electrochemical Performances of P2-Type Layered Oxides for Sodium-Ion Batteries

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Rapp, Philip ; Xu, Mingfeng ; Langella, Aniello ; Gasteiger, Hubert A. ; Bianchini, Matteo:
The Impact of Lithium Substitution on the Gassing Behavior and Electrochemical Performances of P2-Type Layered Oxides for Sodium-Ion Batteries.
In: Journal of the Electrochemical Society. Bd. 173 (2026) Heft 13 . - 130502.
ISSN 1945-7111
DOI: https://doi.org/10.1149/1945-7111/ae7e57

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Abstract

Li-substitution has been studied as an effective strategy to improve the structural stability and activate the O-redox in P2-type layered oxides as cathode materials for sodium-ion batteries. The O-redox process leads to hysteresis during cycling and potentially triggers O2 release. To elucidate the impact of Li-doping on the gassing behavior and electrochemical performance of P2-type layered oxides, we study here three materials with different Li contents (0, 2/18, 3/18 Li/f.u.). OCV hysteresis experiments reveal that the hysteresis increases with Li amount and exhibits an SOC-dependence. Voltage window-opening tests show that hysteresis emerges only after the activation above 4.0 V, which via DFT calculations can be related to Li migration. Rietveld refinements indicate markedly reduced O occupancy in all samples when charged to 4.5 V, confirming that the OCV hysteresis is related to oxygen activity. OEMS analysis provides direct evidence of lattice oxygen loss, showing O2 and CO2 evolution during the first charge in all samples, which increases with Li-doping. While moderate Li-substitution (2/18 Li/f.u.) activates O-redox at a similar onset voltage as the undoped one, higher Li content triggers O-redox at a lower voltage. Long-term cycling of pseudo half-cells and rate capability tests demonstrate the improved electrochemical performance upon Li-substitution, but also imply the necessity to optimize the amount of Li for a balanced O-redox contribution and long-term reversibility.