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Analysis of oxygen behavior upon Na2O oxidation in NNO. a) The top panel shows the galvanostatic charge curve for the initial charging process of the NNO presodiation agent cathode at a current density of 50 mA g⁻¹. Five points are labeled in the charge curve: OCV, 3.25 V,3.45 V, 3.65 V, and 4.5 V, respectively. b) The middle panel shows OEMS results of corresponding time‐resolved evolution rates for O2 and CO2 during initial charging. c) TMS result: amounts of O2 and CO2 collected from the NNO presodiation agent plates with different specific voltages. d) O K‐edge XANES spectra of the NNO presodiation agent cathode and standard samples at TEY modes. The peak at 533 eV represents oxygen in the antifluorite structure of Na2O; the peak at 531.4 eV represents σ* (O─O) peroxide species; and the peak at 531.2 eV represents the hybridized state of O 2p and Ni 3d orbitals in NiO. e) The schematic diagram illustrating the dynamics of electrochemical transfer oxidation process during the charging of Ni–Na2O. The electronic structure of Na2O exhibits a charge transfer electronic ground state in the reduced phase (left). The O (2p) lone pairs denote |O2p. The splitting of the O 2p narrow band into distinct σ, π, π*, and σ* states is illustrated by the red (ΔσO─O) and green (ΔπO─O) arrows, with respect to the conversion of O─O dimer species (bottom horizontal axis).
Source publication
Compensating for the irreversible loss of limited active sodium (Na) is crucial for enhancing the energy density of practical sodium‐ion batteries (SIBs) full‐cell, especially when employing hard carbon anode with initially lower coulombic efficiency. Introducing sacrificial cathode presodiation agents, particularly those that own potential anionic...
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In order to improve the specific capacity of intercalation electrodes for sodium-ion batteries, it is necessary to identify materials capable of storing Na⁺ ions by activating multi-electron redox reactions. Herein, we report a NaFeVPO4(SO4)2 compound as a multi-electron electrode that combines the most abundant Fe and V ions, having multiple oxida...
Citations
More and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths‐of‐discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium‐rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low‐DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD‐dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (On‐). Upon low‐DOD cycling, the accumulation of On‐ and the persistent presence of vacancies in the transition metal (TM) layer intensified the in‐plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out‐of‐plane TM migration. As a result, the aggravated structural degradation of LRLO at low‐DOD impeded reversible Li+ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On‐ persistently corroded the electrode‐electrolyte interface, especially negative for pouch‐type full‐cells with the shuttle effect. Once the “double‐edged sword” effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.
More and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths‐of‐discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium‐rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low‐DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD‐dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (Oⁿ⁻). Upon low‐DOD cycling, the accumulation of Oⁿ⁻ and the persistent presence of vacancies in the transition metal (TM) layer intensified the in‐plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out‐of‐plane TM migration. As a result, the aggravated structural degradation of LRLO at low‐DOD impeded reversible Li⁺ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of Oⁿ⁻ persistently corroded the electrode‐electrolyte interface, especially negative for pouch‐type full‐cells with the shuttle effect. Once the “double‐edged sword” effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.
