“Just a pinch” of salt can improve battery performance


Battery salt 5af984d302cf4When an MOF is carbonised it transforms into a nano-diatom like the way a dragon egg, when given fire-treatment, turns into a fire-born dragon in Game of Thrones. Credit: Dr Jingwei Hou

 

Researchers at Queen Mary University of London, University of Cambridge and Max Planck Institute for Solid State Research have discovered how a pinch of salt can be used to drastically improve the performance of batteries.

They found that adding salt to the inside of a supermolecular sponge and then baking it at a high temperature transformed the sponge into a  based structure.

Surprisingly, the salt reacted with the sponge in special ways and turned it from a homogeneous mass to an intricate structure with fibres, struts, pillars and webs. This kind of 3-D hierarchically organised carbon structure has proven very difficult to grow in a laboratory but is crucial in providing unimpeded ion transport to active sites in a battery.

In the study, published in JACS (Journal of the American Chemical Society), the researchers demonstrate that the use of these  in Lithium-ion batteries not only enables the batteries to be charged-up rapidly, but also at one of the highest capacities.

Due to their intricate architecture the researchers have termed these structures ‘nano-diatoms’, and believe they could also be used in  and conversion, for example as electrocatalysts for hydrogen production.

Lead author and project leader Dr. Stoyan Smoukov, from Queen Mary’s School of Engineering and Materials Science, said: “This metamorphosis only happens when we heat the compounds to 800 degrees centigrade and was as unexpected as hatching fire-born dragons instead of getting baked eggs in the Game of Thrones. It is very satisfying that after the initial surprise, we have also discovered how to control the transformations with chemical composition.”

Carbon, including graphene and carbon nanotubes, is a family of the most versatile materials in nature, used in catalysis and electronics because of its conductivity and chemical and thermal stability.

3-D carbon-based nanostructures with multiple levels of hierarchy not only can retain useful physical properties like good electronic conductivity but also can have unique properties. These 3-D carbon-based materials can exhibit improved wettability (to facilitate ion infiltration), high strength per unit weight, and directional pathways for fluid transport.

It is, however, very challenging to make carbon-based multilevel hierarchical structures, particularly via simple chemical routes, yet these structures would be useful if such materials are to be made in large quantities for industry.

The supermolecular sponge used in the study is also known as a metal organic framework (MOF) material.

These MOFs are attractive, molecularly designed porous materials with many promising applications such as gas storage and separation. The retention of high surface area after carbonisation – or baking at a high temperature—makes them interesting as electrode materials for batteries.

However, so far carbonising MOFs has preserved the  of the initial particles like that of a dense carbon foam. By adding salts to these MOF sponges and carbonising them, the researchers discovered a series of carbon-based materials with multiple levels of hierarchy.

Dr. R. Vasant Kumar, a collaborator on the study from University of Cambridge, commented: “This work pushes the use of the MOFs to a new level. The strategy for structuring carbon materials could be important not only in energy storage but also in energy conversion, and sensing.”

Lead author, Tiesheng Wang (王铁胜), from University of Cambridge, said: “Potentially, we could design nano-diatoms with desired structures and active sites incorporated in the carbon as there are thousands of MOFs and salts for us to select.”

 Explore further: Full of hot air and proud of it: Improving gas storage with MOFs

More information: Tiesheng Wang et al. Bottom-up Formation of Carbon-Based Structures with Multilevel Hierarchy from MOF–Guest Polyhedra, Journal of the American Chemical Society (2018). DOI: 10.1021/jacs.8b02411

Read more at: https://phys.org/news/2018-05-scientists-salt-battery.html#jCp

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nanoparticle discovery could hail revolution in nanotube manufacturing


NANOSPHERES(Nanowerk News) A nanoparticle shaped like a spiky  ball, with magnetic properties, has been uncovered in a new method of  synthesising carbon nanotubes by physicists at Queen Mary University of London  and the University of Kent (“Boundary layer chemical vapor synthesis of  self-organized radial filled-carbon-nanotube structures”).

Sea Urchin nanoparticle

Sea Urchin Nanoparticle

Carbon nanotubes are  hollow, cylindrical molecules that can be manipulated to give them useful  properties. The nanoparticles were discovered accidentally on the rough surfaces  of a reactor designed to grow carbon nanotubes.

Described  as sea urchins because of their characteristic spiny appearance, the particles  consist of nanotubes filled with iron, with equal lengths pointing outwards in  all directions from a central particle.

The  presence of iron and the unusual nanoparticle shape could have potential for a  number of applications, such as batteries that can be charged from waste heat,  mixing with polymers to make permanent magnets, or as particles for cancer  therapies that use heat to kill cancerous cells.

The researchers  found that the rough surfaces of the reactor were covered in a thick powder of  the new nanoparticles and that intentional roughening of the surfaces produced  large quantities of the sea urchin nanoparticles.

“The surprising conclusion is that the sea urchin nanoparticles  grow in vapour by a mechanism that’s similar to snowflake formation. Just as  moist air flowing over a mountain range produces turbulence which results in a  snowfall, the rough surface disrupts a flow to produce a symmetrical and ordered  nanoparticle out of chaotic conditions,” said Dr Mark Baxendale from Queen  Mary’s School of Physics and Astronomy.
On analysis, the researchers found that a small fraction of the  iron inside the carbon nanotubes was a particular type usually only found in  high temperature and pressure conditions.
Dr Baxendale added: “We were surprised to see this rare kind of  iron inside the nanotubes. While we don’t know much about its behaviour, we can  see that the presence of this small fraction of iron greatly influences the  magnetic properties of the nanoparticle.”
Source: Queen Mary University of London

Read more: http://www.nanowerk.com/news2/newsid=32172.php#ixzz2eXAe8uxY