- Email: [email protected]
Improving sodium–metal sulfide batteries
NEWS
photoanode to discover another 12 metal oxide materials as part of the Materials Genome Initiative. The research expands considerably the number of known photoelectrocatalysts for water oxidation, and establishes ternary metal vanadates as a useful class of photoanode materials – which can split water using visible light as an energy source – to generate chemical fuels from sunlight. It
Materials Today Volume 20, Number 5 June 2017
also shows their high-throughput theory – experiment pipeline is an effective approach to materials discovery, and the correlation between structure motif, electronic structure and the photocatalytic properties of a many novel vanadate photoanodes. The combination of complementary techniques involved provides a potential blueprint for research. As Qimin Yan said, ‘‘The materials discovery pipeline is a first-
time demonstration of integrating theory and experiment to discovery a host of new functional materials’’, a breakthrough that impacts a broad suite of technologies necessary for realizing future industrial energy production. The team now plan to continue the search for stable and efficient transition metal oxide photoanodes in other chemical spaces. Laurie Donaldson
NEWS
Improving sodium–metal sulfide batteries A new study investigating the chemical fundamentals, performance and microstructural defects of sodium–metal sulfide batteries has shown how the material changes during the charge/discharge process, insight that could lead to innovative battery design and optimization of materials microstructure for future energy storage needs. Although most portable electronics are now powered by rechargeable lithium–ion batteries, the technology is constrained by the high cost and limited availability of lithium, leading to much research into alternatives. Sodium is seen as a potential candidate due to its cheapness, availability and similar chemical properties, but sodium–ion batteries go through changes in their charge and discharge cycles, degrading their performance. The research, published in Advanced Energy Materials [Wang, et al., Adv. Energy Mater. (2017), doi:10.1002/aenm. 201602706], used full-field transmission X-ray microscopy (TXM) to ensure nanoscale spatial resolution and a large field of view to image the insertion of sodium ions
into, and extracted from, an iron sulfide electrode over 10 cycles, the first time that the structural and chemical evolution of sodium–metal sulfide batteries have been captured during their electrochemical reactions. The team, from US DoE’s Brookhaven National Laboratory, found the loss in battery capacity was due largely to sodium ions entering and leaving iron sulfide, the electrode material used, from substantial cracks originating at the surface of the iron sulfide particles during the first charge/discharge cycle. The electrochemical reactions resulted in irreversible changes in the microstructure and chemical composition of the electrode; as iron sulphide has a high theoretical energy density, it is hoped that showing the underlying mechanism limiting performance will help to improve its real energy density. They mapped the corresponding chemical changes using TXM combined with X-ray absorption near edge structure, where X-rays are fine-tuned to the energy at which there is a sharp decrease in the amount of
X-rays that a chemical element absorbs. As such energy is specific to each element, the absorption spectra can identify chemical composition, showing that the iron sulfide particles experience a chemical transformation following the same surface-to-core mechanism as found in the microstructural defects. As team leader Jun Wang said, ‘‘It appears that . . . the cracks and fractures created by volume expansion of the iron sulfide particles during discharge destroy the particles’ structure. . . On the other hand, these defects provide a path for sodium ions to get to the particles’ core’’. As volume shrinks during charging, some paths are blocked, which restricts the movement of sodium ions, trapping some in the core. The researchers will now look for ways to improve battery capacity after the first cycle, and the results have inspired them to look at nanoengineering approaches to decrease interfacial resistance and ion diffusion barriers to enhance cycle reversibility of conversion-based battery materials. Laurie Donaldson
New process for 3D printing of cellulose Despite cellulose being the most abundant organic polymer in the world and the basis of paper, its use in additive manufacturing has faced difficulties. However, two scientists at MIT have developed a new method that could provide a viable alternative to the polymers currently used in 3D printing materials, with potential applications in the many industries that use cellulosic materials and would benefit from the customization that additive manufacturing brings. As extrusion-based 3D printers depend on heating polymer to make it flow, production speed is constrained by the amount of
224
heat that can be delivered to the polymer without damaging it. While cellulose is biodegradable, biorenewable, biocompatible, mechanically robust and chemically very versatile, on heating it thermally decomposes before becoming flowable, partially due to hydrogen bonds between the cellulose molecules. This intermolecular bonding makes high-concentration cellulose solutions very viscous and therefore not easy to extrude. As reported in the journal Advanced Materials Technologies [S.W. Pattinson, A.J. Hart, Adv. Mater. Technol. (2017) doi:10.1002/
admt.201600084], to overcome this problem, the researchers A. John Hart and Sebastian Pattinson used cellulose acetate, which in bulk is as cheap as thermoplastics used for injection molding, and cheaper than the usual filament materials used for 3D printing. Cellulose acetate can be dissolved in acetone before being extruded – as the acetone evaporates quickly, the cellulose acetate solidifies in position, while another treatment replaces the acetate groups and increases the strength of the printed parts. In a fully room-temperature process, after 3D printing, they restored the hydrogen
photoanode to discover another 12 metal oxide materials as part of the Materials Genome Initiative. The research expands considerably the number of known photoelectrocatalysts for water oxidation, and establishes ternary metal vanadates as a useful class of photoanode materials – which can split water using visible light as an energy source – to generate chemical fuels from sunlight. It
Materials Today Volume 20, Number 5 June 2017
also shows their high-throughput theory – experiment pipeline is an effective approach to materials discovery, and the correlation between structure motif, electronic structure and the photocatalytic properties of a many novel vanadate photoanodes. The combination of complementary techniques involved provides a potential blueprint for research. As Qimin Yan said, ‘‘The materials discovery pipeline is a first-
time demonstration of integrating theory and experiment to discovery a host of new functional materials’’, a breakthrough that impacts a broad suite of technologies necessary for realizing future industrial energy production. The team now plan to continue the search for stable and efficient transition metal oxide photoanodes in other chemical spaces. Laurie Donaldson
NEWS
Improving sodium–metal sulfide batteries A new study investigating the chemical fundamentals, performance and microstructural defects of sodium–metal sulfide batteries has shown how the material changes during the charge/discharge process, insight that could lead to innovative battery design and optimization of materials microstructure for future energy storage needs. Although most portable electronics are now powered by rechargeable lithium–ion batteries, the technology is constrained by the high cost and limited availability of lithium, leading to much research into alternatives. Sodium is seen as a potential candidate due to its cheapness, availability and similar chemical properties, but sodium–ion batteries go through changes in their charge and discharge cycles, degrading their performance. The research, published in Advanced Energy Materials [Wang, et al., Adv. Energy Mater. (2017), doi:10.1002/aenm. 201602706], used full-field transmission X-ray microscopy (TXM) to ensure nanoscale spatial resolution and a large field of view to image the insertion of sodium ions
into, and extracted from, an iron sulfide electrode over 10 cycles, the first time that the structural and chemical evolution of sodium–metal sulfide batteries have been captured during their electrochemical reactions. The team, from US DoE’s Brookhaven National Laboratory, found the loss in battery capacity was due largely to sodium ions entering and leaving iron sulfide, the electrode material used, from substantial cracks originating at the surface of the iron sulfide particles during the first charge/discharge cycle. The electrochemical reactions resulted in irreversible changes in the microstructure and chemical composition of the electrode; as iron sulphide has a high theoretical energy density, it is hoped that showing the underlying mechanism limiting performance will help to improve its real energy density. They mapped the corresponding chemical changes using TXM combined with X-ray absorption near edge structure, where X-rays are fine-tuned to the energy at which there is a sharp decrease in the amount of
X-rays that a chemical element absorbs. As such energy is specific to each element, the absorption spectra can identify chemical composition, showing that the iron sulfide particles experience a chemical transformation following the same surface-to-core mechanism as found in the microstructural defects. As team leader Jun Wang said, ‘‘It appears that . . . the cracks and fractures created by volume expansion of the iron sulfide particles during discharge destroy the particles’ structure. . . On the other hand, these defects provide a path for sodium ions to get to the particles’ core’’. As volume shrinks during charging, some paths are blocked, which restricts the movement of sodium ions, trapping some in the core. The researchers will now look for ways to improve battery capacity after the first cycle, and the results have inspired them to look at nanoengineering approaches to decrease interfacial resistance and ion diffusion barriers to enhance cycle reversibility of conversion-based battery materials. Laurie Donaldson
New process for 3D printing of cellulose Despite cellulose being the most abundant organic polymer in the world and the basis of paper, its use in additive manufacturing has faced difficulties. However, two scientists at MIT have developed a new method that could provide a viable alternative to the polymers currently used in 3D printing materials, with potential applications in the many industries that use cellulosic materials and would benefit from the customization that additive manufacturing brings. As extrusion-based 3D printers depend on heating polymer to make it flow, production speed is constrained by the amount of
224
heat that can be delivered to the polymer without damaging it. While cellulose is biodegradable, biorenewable, biocompatible, mechanically robust and chemically very versatile, on heating it thermally decomposes before becoming flowable, partially due to hydrogen bonds between the cellulose molecules. This intermolecular bonding makes high-concentration cellulose solutions very viscous and therefore not easy to extrude. As reported in the journal Advanced Materials Technologies [S.W. Pattinson, A.J. Hart, Adv. Mater. Technol. (2017) doi:10.1002/
admt.201600084], to overcome this problem, the researchers A. John Hart and Sebastian Pattinson used cellulose acetate, which in bulk is as cheap as thermoplastics used for injection molding, and cheaper than the usual filament materials used for 3D printing. Cellulose acetate can be dissolved in acetone before being extruded – as the acetone evaporates quickly, the cellulose acetate solidifies in position, while another treatment replaces the acetate groups and increases the strength of the printed parts. In a fully room-temperature process, after 3D printing, they restored the hydrogen