May
16
Queen Mary University of London researchers have discovered how a pinch of salt can be used to drastically improve the performance of lithium ion batteries. They added salt to the inside of a supermolecular sponge and then baked it at a high temperature transforming the sponge into a carbon-based structure.
Surprisingly, the salt reacted with the sponge in special ways and turned it from a homogeneous mass to an intricate structure with fibers, struts, pillars and webs. This kind of 3D hierarchically organized 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.
Image Credit: Dr. Jingwei Hou, Queen Mary University of London. Click image for the largest view.
In the study, published in JACS (Journal of the American Chemical Society), the researchers demonstrate that the use of these materials 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 energy storage 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 800ยบ C 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.
3D 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 3D 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 carbonizing MOFs has preserved the structure of the initial particles like that of a dense carbon foam. By adding salts to these MOF sponges and carbonizing 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, 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.”
The press release isn’t saying how the group came upon the idea. We’ll simply think it was immense intellectual prowess, in lieu of spontaneous serendipity with astute observational skills. Its welcome process engineering, indeed. One hopes this technology gets long legs for commercial scale, and soon.
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Surprisingly, the salt reacted with the sponge in special ways and turned it from a homogeneous mass to an intricate structure with fibers, struts, pillars and webs.