Magnesium-ion batteries hold promise as next-generation secondary battery systems owing to its low cost, safety and high volumetric capacity. Magnesium metal silicates exhibit potential electrode ...materials with high specific capacities. However, the strong electrostatic interaction between Mg2+ and host lattice due to its divalency as well as antisite cation exchange, induces slow intercalation kinetics of Mg ions within the crystal lattices. Thus, nanocrystalline particles with shortened Mg ion diffusion distance enable the insertion/extraction of Mg ions and improve specific capacities of the batteries. Herein, we report the low-temperature production of crystalline MgMnSiO4 and MgCoSiO4 nanoparticles by a rapid supercritical fluid processing. The extraction of magnesium ions from the olivine framework has been confirmed by X-ray photoelectron spectroscopy, revealing its ability as active materials for magnesium-ion battery.
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•The low-temperature production of MgMnSiO4 and MgCoSiO4 nanoparticles.•A rapid supercritical fluid processing synthesis.•The extraction of magnesium from the olivine framework in Mg-ion battery.•Samples was studied by X-ray photoelectron spectroscopy.
•Al-substituted MgMn2O4 nanoparticles are synthesized by a sol-gel method.•MgMn2-xAlxO4 has both tetragonal and cubic spinel phases.•The fraction of cubic spinel phase tends to increase with the Al ...ratio.•MgMn2-xAlxO4 exhibits higher discharge capacity than normal MgMn2O4.•The increase in cubic phase fraction reduces structural change during discharging.
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Magnesium rechargeable batteries using Mg-metal anodes are promising post-lithium-ion batteries. MgMn2O4 is a strong candidate cathode material owing to its high energy density and relatively high Mg2+-ion diffusivity. However, while pristine MgMn2O4 forms a tetragonal spinel structure (I41/amd) owing to the Jahn–Teller effect of Mn3+, it adopts a cubic structure in the charged/discharged state. This results in a structural change from tetragonal to cubic during charge/discharge cycling, leading to poor battery performance and reversibility. To improve the cathode performance, we prepared Al-substituted MgMn2−xAlxO4 spinel (x = 0, 0.1, 0.2, 0.5) to suppress the Jahn–Teller distortion. The obtained MgMn2−xAlxO4 spinel is a two-phase crystal with coexisting tetragonal and cubic spinel structures, whereby the fraction of cubic phase tends to increase with the Al ratio. The Al-substituted spinels exhibit superior discharge capacities to that of MgMn2O4. The increase in cubic spinel phase fraction by Al-substitution and the reduced structural change during discharging will aid the development of superior cathodes for magnesium batteries.
Novel ultrathin Li2MnSiO4 nanosheets have been prepared in a rapid one pot supercritical fluid synthesis method. Nanosheets structured cathode material exhibits a discharge capacity of ∼340 mAh/g at ...45 ± 5 °C. This result shows two lithium extraction/insertion performances with good cycle ability without any structural instability up to 20 cycles. The two-dimensional nanosheets structure enables us to overcome structural instability problem in the lithium metal silicate based cathode materials and allows successful insertion/extraction of two complete lithium ions.
Molybdenum sulfides are very attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) from water. The atomic structure and identity of the catalytically active sites ...have been well established for crystalline molybdenum disulfide (c-MoS2) but not for amorphous molybdenum sulfide (a-MoSx), which exhibits significantly higher HER activity compared to its crystalline counterpart. Here we show that HER-active a-MoSx, prepared either as nanoparticles or as films, is a molecular-based coordination polymer consisting of discrete Mo3S13(2-) building blocks. Of the three terminal disulfide (S2(2-)) ligands within these clusters, two are shared to form the polymer chain. The third one remains free and generates molybdenum hydride moieties as the active site under H2 evolution conditions. Such a molecular structure therefore provides a basis for revisiting the mechanism of a-MoSx catalytic activity, as well as explaining some of its special properties such as reductive activation and corrosion. Our findings open up new avenues for the rational optimization of this HER electrocatalyst as an alternative to platinum.
Rechargeable Mg-ion batteries have gained significant attention as promising alternatives to Li-ion batteries. Owing to its high theoretical energy density and relatively high Mg-ion diffusivity, ...spinel oxide MgMn2O4 is a viable candidate as a cathode material; however, its poor rate capability limits its applicability. Decreasing the particle size can effectively address this problem by enhancing Mg-ion diffusion. In this paper, we demonstrate the conventional solvothermal synthesis of MgMn2O4 spinel nanoparticles. Solvothermal process is one of the most fundamental methods for nanoparticle synthesis because of its simple and flexible synthetic conditions. In the alcohol solvothermal conditions, spinel type MgMn2O4 nanoparticles of approximately 10–15 nm are successfully synthesized using amorphous MnO2 as a precursor. We note that controlling Mg2+ solvation and oxidation/reduction conditions in the reaction solution is crucial for the effective intercalation of Mg2+ into the MnO6 octahedral framework. Although the obtained MgMn2O4 nanoparticles aggregate to form submicron secondary particles, the aggregation can be suppressed by compositing them with the carbon nanotubes dispersed in the reaction solution. The composite exhibits a discharge capacity of 60 mAh g−1 with maintaining 80% of capacity retention after the 10th cycle.
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•MgMn2O4 spinel nanoparticles were selectively synthesized by reductive solvothermal process.•Reductive reaction and dehydrated solvation of Mg2+ are preferable for wet-process synthesis.•MgMn2O4-carbon nanotube composite was obtained by a one-pot solvothermal route.•The composite exhibited improved cathode performances at room temperature.
Graphene nanosheet (GNS) gives rise to an extraordinary modification to the properties of Pt cluster electrocatalysts supported on it. The Pt/GNS electrocatalyst revealed an unusually high activity ...for methanol oxidation reaction compared to Pt/carbon black catalyst. The Pt/GNS electrocatalyst also revealed quite a different characteristic for CO oxidation among the measured catalyst samples. It is found that Pt particles below 0.5 nm in size are formed on GNS, which would acquire the specific electronic structures of Pt, modifying its catalytic activities.
Solid-state cells are one of the strongest candidate designs for utilisation of renewable high-capacity organic cathode materials. Following our previous work on tetracyanoquinodimethane, further ...high-capacity quinonic compounds, namely dichlorodicyanobenzoquinone, tetrahydroxybenzoquinone and dihydroxybenzoquinone were investigated. Cell cycling experiments indicated that these compounds undergo reversible redox reaction with significantly less cyclic capacity decay. 3.4 V of cell voltage was attainable from DDQ cells and capacities exceeding 250 mAh g−1 were obtained from THBQ and DHBQ. These results reassure that by adopting an appropriate battery design, cycleability of organic cathodes can be drastically improved and they can be exploited as low-cost environmentally friendly high energy-density cathode materials.
► Three high energy-density quinonic cathode compounds were incorporated in solid-state organic cathode batteries. ► The cycleabilities of organic cathode cells were improved by nearly two orders of magnitude compared to conventional cells. ► The general applicability of organic cathode solid-state cells was demonstrated. ► Compounds that have been regarded “unusable” became “usable” under novel cell design and construction.
Supercapacitors, which can be charged/discharged rapidly, play important roles in a sustainable society. Thick electrodes can reduce the ratio of inactive components in the overall cell while ...simultaneously improving energy and power densities. However, thick electrodes induce longer ion diffusion pathways, and capacitance drops dramatically after a certain thickness. To overcome this, precisely designed macro‐ and nano‐porous 3D‐hierarchical carbon lattices, where ions can diffuse freely inside the electrode, are prepared by combining an inexpensive stereolithography‐type 3D printer, whose resolution is 50 µm, with a simple CO2 activation process. The activated 3D carbon lattice with a 66% burn‐off ratio (3D‐CL‐A66%) has ordered macropores (≈150 µm) and uniform nanopores (2–3 nm), exhibiting a maximum areal capacitance of 5251 mF cm–2 at 3 mA cm–2. Furthermore, manganese oxide is electrochemically deposited on 3D‐CL‐A16% for 8 min (3D‐CL‐A16%‐MnO2‐8 min), increasing the areal capacitance by 2.5‐times. Finally, an all‐3D‐printed asymmetric 1.8 V supercapacitor is prepared by combining 3D‐CL‐A16%‐MnO2‐8 min and 3D‐CL‐A66% as the positive and negative electrodes, respectively, demonstrating a maximum energy density of 0.808 mWh cm–2 at a power density of 2.48 mW cm–2. The achieved values are one of the highest areal energy and power densities reported so far.
A 3D‐hierarchical carbon lattice with ordered macropores (≈150 µm) and uniform nanopores (2–3 nm) for supercapacitor electrodes is successfully prepared using an inexpensive 3D printer and a simple gas activation process. The 3D‐ordered macropores facilitate ion transport inside the thick electrodes. The achieved areal energy and power densities are among the highest values reported to date.
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