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Contrary to molecular species, only very few solids are reported to host manganese (V) species. Herein, we report three new compounds with a hydroxyapatite structural backbone built on the MnVO4 3− anion: Sr5[(Mn1−xSix)O4]3(OH)1−3x (x = 0 and 0.053), Sr5(MnO4)3(OH)1−yFy (y = 0.90), and Sr5[(Mn1−xSix)- O4]3F1−3x (x = 0.058). These solids are fully characterized using powder X-ray and neutron powder diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy (EELS), thermogravimetric analysis, and magnetic measurements. Especially, we report for the first time EELS Mn−L2,3 spectra of manganese with the oxidation state (V). Contrary to other Mn(V) oxides, these solids and the nominal compound Sr5(MnO4)3OH do not comprise Ba2+ cations but rely only on Sr2+ cations, showing that barium is not a required element to stabilize Mn(V) species in inorganic solids. We show that by tuning soft chemistry conditions on the one hand and post-treatment topological transformation conditions on the other hand, Mn(V) and hydroxyl groups can be substituted by Si(IV) and fluoride ions, respectively. Hence, we deliver solids with a potentially wide composition range. These compounds show significant oxygen anionic conduction, thus suggesting the emergence of new functional materials built from high-oxidation state manganese cations., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Contrary to molecular species, only very few solids are reported to host manganese (V) species. Herein, we report three new compounds with a hydroxyapatite structural backbone built on the MnVO43– anion: Sr5[(Mn1–xSix)O4]3(OH)1–3x (x = 0 and 0.053), Sr5(MnO4)3(OH)1–yFy (y = 0.90), and Sr5[(Mn1–xSix)O4]3F1–3x (x = 0.058). These solids are fully characterized using powder X-ray and neutron powder diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy (EELS), thermogravimetric analysis, and magnetic measurements. Especially, we report for the first time EELS Mn–L2,3 spectra of manganese with the oxidation state (V). Contrary to other Mn(V) oxides, these solids and the nominal compound Sr5(MnO4)3OH do not comprise Ba2+ cations but rely only on Sr2+ cations, showing that barium is not a required element to stabilize Mn(V) species in inorganic solids. We show that by tuning soft chemistry conditions on the one hand and post-treatment topological transformation conditions on the other hand, Mn(V) and hydroxyl groups can be substituted by Si(IV) and fluoride ions, respectively. Hence, we deliver solids with a potentially wide composition range. These compounds show significant oxygen anionic conduction, thus suggesting the emergence of new functional materials built from high-oxidation state manganese cations., Depto. de Química Inorgánica, Fac. de Ciencias Químicas, TRUE, pub

Material abundance and eco-efficient synthetic protocols are becoming the overriding factors for developing sustainable Li-ion batteries, and hence today there is great interest in LiFePO4. The recently reported tavorite-type LiFeSO4F cathode material, which shows a redox potential of 3.6 V and a practical capacity of similar to 130 mA h g-1 without the need for sophisticated carbon coating or particle downsizing, stands presently as a serious contender to LiFePO4. However, its synthesis is still not routinely reproducible. Herein, we offer a direct explanation by showing the strong effect of the room temperature relative humidity on both LiFeSO4F aging stability and its electrochemical performances. We demonstrate the complete degradation of tavorite-type LiFeSO4F into FeSO4 · nH2O (n = 1, 4, 7) and LiF in environments with relative humidities greater than 62%, and also show the feasibility of triggering in situ formation of a F--free (Li)FeSO4OH phase within the cell. This work, which we also extend to the 3.9 V triplite-type LiFeSO4F polymorph, provides a foundation for achieving the consistent production and handling of LiFeSO4F electrodes in view of large-scale manufacturing. This moisture sensitivity issue, which can be mitigated by surface treatments, is inherent to sulfate-based electrode materials and the battery community must be aware of it.

Material abundance and eco-efficient synthetic protocols are becoming the overriding factors for developing sustainable Li-ion batteries, and hence today there is great interest in LiFePO4. The recently reported tavorite-type LiFeSO4F cathode material, which shows a redox potential of 3.6 V and a practical capacity of similar to 130 mA h g-1 without the need for sophisticated carbon coating or particle downsizing, stands presently as a serious contender to LiFePO4. However, its synthesis is still not routinely reproducible. Herein, we offer a direct explanation by showing the strong effect of the room temperature relative humidity on both LiFeSO4F aging stability and its electrochemical performances. We demonstrate the complete degradation of tavorite-type LiFeSO4F into FeSO4 · nH2O (n = 1, 4, 7) and LiF in environments with relative humidities greater than 62%, and also show the feasibility of triggering in situ formation of a F--free (Li)FeSO4OH phase within the cell. This work, which we also extend to the 3.9 V triplite-type LiFeSO4F polymorph, provides a foundation for achieving the consistent production and handling of LiFeSO4F electrodes in view of large-scale manufacturing. This moisture sensitivity issue, which can be mitigated by surface treatments, is inherent to sulfate-based electrode materials and the battery community must be aware of it.

Material abundance and eco-efficient synthetic protocols are becoming the overriding factors for developing sustainable Li-ion batteries, and hence today there is great interest in LiFePO4. The recently reported tavorite-type LiFeSO4F cathode material, which shows a redox potential of 3.6 V and a practical capacity of similar to 130 mA h g-1 without the need for sophisticated carbon coating or particle downsizing, stands presently as a serious contender to LiFePO4. However, its synthesis is still not routinely reproducible. Herein, we offer a direct explanation by showing the strong effect of the room temperature relative humidity on both LiFeSO4F aging stability and its electrochemical performances. We demonstrate the complete degradation of tavorite-type LiFeSO4F into FeSO4 · nH2O (n = 1, 4, 7) and LiF in environments with relative humidities greater than 62%, and also show the feasibility of triggering in situ formation of a F--free (Li)FeSO4OH phase within the cell. This work, which we also extend to the 3.9 V triplite-type LiFeSO4F polymorph, provides a foundation for achieving the consistent production and handling of LiFeSO4F electrodes in view of large-scale manufacturing. This moisture sensitivity issue, which can be mitigated by surface treatments, is inherent to sulfate-based electrode materials and the battery community must be aware of it.

Na2Ti3O7 was recently reported to be highly promising as a negative electrode material for Na-ion batteries, thanks to its very low intercalation voltage (0.3 V vs Na+/Na-0) and high capacity (200 mAh/g). The investigation of the redox mechanism in A(2)Ti(3)O(7) (A = Li, Na) upon additional alkali ion intercalation concomitant to reduction of titanium is reported in this paper. Even if the low stability of the reduced phases (A(2+x),Ti3O7) precluded a direct study, density functional theory (DFT) calculations allowed us to propose structural models for the reduced phases (A(2+x)Ti(3)O(7)), which were further successfully confronted to the available experimental data. The alkali atoms are octahedrally coordinated in the reduced A(2+x)Ti(3)O(7) phase, so that the whole resulting structure can be considered rocksalt type. The very different potentials at which ion insertion is observed for A = Li or A = Na clearly prove that analogies between lithium and sodium systems cannot be taken for granted. In this case, such findings can be fully rationalized through DFT and arise from the differences in polarizing character between lithium and sodium ions that cause, respectively, contraction and expansion of the cell volume and the destabilization of the inserted materials derived from the larger size of sodium ions.

Na2Ti3O7 was recently reported to be highly promising as a negative electrode material for Na-ion batteries, thanks to its very low intercalation voltage (0.3 V vs Na+/Na-0) and high capacity (200 mAh/g). The investigation of the redox mechanism in A(2)Ti(3)O(7) (A = Li, Na) upon additional alkali ion intercalation concomitant to reduction of titanium is reported in this paper. Even if the low stability of the reduced phases (A(2+x),Ti3O7) precluded a direct study, density functional theory (DFT) calculations allowed us to propose structural models for the reduced phases (A(2+x)Ti(3)O(7)), which were further successfully confronted to the available experimental data. The alkali atoms are octahedrally coordinated in the reduced A(2+x)Ti(3)O(7) phase, so that the whole resulting structure can be considered rocksalt type. The very different potentials at which ion insertion is observed for A = Li or A = Na clearly prove that analogies between lithium and sodium systems cannot be taken for granted. In this case, such findings can be fully rationalized through DFT and arise from the differences in polarizing character between lithium and sodium ions that cause, respectively, contraction and expansion of the cell volume and the destabilization of the inserted materials derived from the larger size of sodium ions.