| 1. |
- Guerrini, Niccolo, et al.
(författare)
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Charging Mechanism of Li2MnO3
- 2020
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 32:9, s. 3733-3740
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Tidskriftsartikel (refereegranskat)abstract
- Operando mass spectroscopy demonstrates quantitatively that lithium extraction from Li2MnO3 is charge compensated by oxygen loss (O-loss) not oxidation of oxide ions that are retained within the structural framework (O-redox). This fact is confirmed by X-ray absorption and emission spectroscopy. Li NMR shows that the two-phase core-shell structure, which forms on charging, is composed of an intact Li2MnO3 core and a highly disordered shell containing no Li, with a composition close to MnO2. Discharge involves Li insertion into the disordered shell. CO2 and O-2 are detected on charging at 15 mA g(-1), whereas charging by galvanostatic intermittent titration technique (GITT) forms only CO2; an observation in agreement with the previously described model of oxygen evolution from high-voltage cathodes producing singlet O-2 that reacts with the electrolyte forming CO2. The dominance of oxygen evolution over O-redox is in accordance with the model of O-loss occurring when the oxide ions are undercoordinated; O in the shell devoid of Li is coordinated by only 2 Mn.
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| 2. |
- House, Robert A., et al.
(författare)
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Lithium manganese oxyfluoride as a new cathode material exhibiting oxygen redox
- 2018
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 11:4, s. 926-932
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Tidskriftsartikel (refereegranskat)abstract
- The quantity of charge stored in transition metal oxide intercalation cathodes for Li or Na batteries is not limited by transition metal redox reactions but can also access redox reactions on O; examples include Li1.2Ni0.13Mn0.54Co0.13O2, Li2Ru0.75Sn0.25O3, Li1.2Nb0.3Mn0.4O2, Na2RuO3 and Na2/3Mg0.28Mn0.72O2. Here we show that oxyfluorides can also exhibit charge storage by O-redox. We report the discovery of lithium manganese oxyfluoride, specifically the composition, Li1.9Mn0.95O2.05F0.95, with a high capacity to store charge of 280 mA h g(-1) (corresponding to 960 W h kg(-1)) of which almost half, 130 mA h g(-1), arises from O-redox. This material has a disordered cubic rocksalt structure and the voltage-composition curve is significantly more reversible compared with ordered Li-rich layered cathodes. Unlike lithium manganese oxides such as the ordered layered rocksalt Li2MnO3, Li1.9Mn0.95O2.05F0.95 does not exhibit O loss from the lattice. The material is synthesised using a simple, one-pot mechanochemical procedure.
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