Lithium Manganese Sulfates as a New Class of Supercapattery Materials at Elevated Temperatures

To make supercapattery devices feasible, there is an urgent need to find electrode materials that exhibit a hybrid mechanism of energy storage. Herein, we provide a first report on the capability of lithium manganese sulfates to be used as supercapattery materials at elevated temperatures. Two compositions are studied: monoclinic Li$_2$Mn(SO$_4$)$_2$ and orthorhombic Li$_2$Mn$_2$(SO$_4$)$_3$, which are prepared by a freeze-drying method followed by heat treatment at 500 °C. The electrochemical performance of sulfate electrodes is evaluated in lithium-ion cells using two types of electrolytes: conventional carbonate-based electrolytes and ionic liquid IL ones. The electrochemical measurements are carried out in the temperature range of 20–60 °C. The stability of sulfate electrodes after cycling is monitored by in-situ Raman spectroscopy and ex-situ XRD and TEM analysis. It is found that sulfate salts store Li+ by a hybrid mechanism that depends on the kind of electrolyte used and the recording temperature. Li$_2$Mn(SO$_4$)$_2$ outperforms Li$_2$Mn$_2$(SO$_4$)$_3$ and displays excellent electrochemical properties at elevated temperatures: at 60 °C, the energy density reaches 280 Wh/kg at a power density of 11,000 W/kg. During cell cycling, there is a transformation of the Li-rich salt, Li$_2$Mn(SO$_4$)$_2$, into a defective Li-poor one, Li$_2$Mn$_2$(SO$_4$)$_3$, which appears to be responsible for the improved storage properties. The data reveals that Li$_2$Mn(SO$_4$)$_2$ is a prospective candidate for supercapacitor electrode materials at elevated temperatures

Metal Substitution versus Oxygen-Storage Modifier to Regulate the Oxygen Redox Reactions in Sodium-Deficient Three-Layered Oxides

Sodium-deficient nickel-manganese oxides with three-layered stacking exhibit the unique property of dual nickel-oxygen redox activity, which allows them to achieve enormous specific capacity. The challenge is how to stabilize the oxygen redox activity during cycling. This study demonstrates that oxygen redox activity of P3-Na2/3Ni1/2Mn1/2O2 during both Na+ and Li+ intercalation can be regulated by the design of oxide architecture that includes target metal substituents (such as Mg2+ and Ti4+) and oxygen storage modifiers (such as CeO2). Although the substitution for nickel with Ti4+ amplifies the oxygen redox activity and intensifies the interaction of oxides with NaPF6- and LiPF6-based electrolytes, the Mg2+ substituents influence mainly the nickel redox activity and suppress the deposition of electrolyte decomposed products (such as MnF2). The CeO2-modifier has a much stronger effect on the oxygen redox activity than that of metal substituents; thus, the highest specific capacity is attained. In addition, the CeO2-modifier tunes the electrode–electrode interaction by eliminating the deposition of MnF2. As a result, the Mg-substituted oxide modified with CeO2 displays high capacity, excellent cycling stability and exceptional rate capability when used as cathode in Na-ion cell, while in Li-ion cell, the best performance is achieved for Ti-substituted oxide modified by CeO2

Metal Substitution versus Oxygen-Storage Modifier to Regulate the Oxygen Redox Reactions in Sodium-Deficient Three-Layered Oxides

Sodium-deficient nickel-manganese oxides with three-layered stacking exhibit the unique property of dual nickel-oxygen redox activity, which allows them to achieve enormous specific capacity. The challenge is how to stabilize the oxygen redox activity during cycling. This study demonstrates that oxygen redox activity of P3-Na2/3Ni1/2Mn1/2O2 during both Na+ and Li+ intercalation can be regulated by the design of oxide architecture that includes target metal substituents (such as Mg2+ and Ti4+) and oxygen storage modifiers (such as CeO2). Although the substitution for nickel with Ti4+ amplifies the oxygen redox activity and intensifies the interaction of oxides with NaPF6- and LiPF6-based electrolytes, the Mg2+ substituents influence mainly the nickel redox activity and suppress the deposition of electrolyte decomposed products (such as MnF2). The CeO2-modifier has a much stronger effect on the oxygen redox activity than that of metal substituents; thus, the highest specific capacity is attained. In addition, the CeO2-modifier tunes the electrode–electrode interaction by eliminating the deposition of MnF2. As a result, the Mg-substituted oxide modified with CeO2 displays high capacity, excellent cycling stability and exceptional rate capability when used as cathode in Na-ion cell, while in Li-ion cell, the best performance is achieved for Ti-substituted oxide modified by CeO2

High-Performance Layered Oxides for Sodium-Ion Batteries Achieved through Combined Aluminum Substitution and Surface Treatment

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migration between layers occurring during oxide cycling was manipulated by oxide morphology. The best cycling stability is observed for Na2/3Ni0.42Al0.08Mn1/2O2 having a column-like morphology of stacked plate-like particles along the common faces. The treatment of the layered oxides with Al2O3 mitigates the Mn dissolution reaction during electrode cycling in the NaPF6-based electrolyte, thus contributing to a high cycling stability

Oxidation of carbon monoxide over Cu1-xCrxCo2O4 in the presence of sulfur oxides

Carbon monoxide oxidation activity and aging of Cu1-xCrxCo2O4 (0<x<1) spinels in the presence of sulfur oxides have been studied. The results obtained indicate that the sulfur tolerance is related to the presence of octahedral Co3+ (Oh) and Cu2+ (Oh) ions in the ternary spinels

Structure and reversible lithium intercalation in a new P′3-phase: Na2/3Mn1−yFeyO2 (y = 0, 1/3, 2/3)

In this contribution, new data on the reversible Li+ intercalation in iron substituted sodium manganates are provided. Novel Na2/3Mn1−yFeyO2 (y = 0, 1/3 and 2/3) compounds with a P′3-type structure are prepared from freeze-dried citrate precursors at 500 °C. A new structural element is the development of three-layer oxygen stacking contrary to the well-known P2-type Na2/3MnO2 with a two-layer sequence. The effect of Fe additives on the structure of Na2/3MnO2 was examined by XRD powder diffraction and TEM analysis. The oxidation state and the distribution of transition metal ions in Na2/3Mn1−yFeyO2 were analysed using electron paramagnetic resonance spectroscopy. The lithium intercalation in Na2/3Mn1−yFeyO2 was investigated in two-electrode lithium cells of the type Li|LiPF6 (EC:DMC)|Na2/3Mn1−yFeyO2. The stability of the layered phases during lithium intercalation was studied by ex situ Raman spectroscopy. It was found that the intermediate Na2/3Mn2/3Fe1/3O2 composition is able to intercalate Li+ reversibly in high amounts. Details of the structure and its stability during the Li+ intercalation are discussed