TPT May 2020

G LOBA L MARKE T P L AC E

G LOBA L MARKE T P L AC E

likely to have defects, such as cracking or distortion, during manufacture,” Easton explained.

Research Materials research goes skin deep

Renewable energy will demand a battery of improvements Finding the key to stable cycling… Researchers at Rice University’s Brown School of Engineering discovered that a layer of alumina applied to common cathodes could be key to improved batteries for electric cars and off-grid energy storage, combining a macro-porous silicon anode with an alumina-coated NMC (nickel-manganese- cobalt) cathode. The research team reported in the journal ACS Applied Energy Materials that a mechanism traps lithium inside batteries, limiting the number of times the battery can be charged and discharged at full power. Conventional lithium- ion batteries use graphite-based anodes with a capacity below 400 milliamp hours per gram (mAh/g). Silicon anodes have up to ten times that capacity, but as silicon expands it alloys with the lithium and stresses the anode. The team’s test batteries indicate that making the silicon porous, and limiting the anode’s capacity to 1,000mAh/g, provides stable cycling with very high capacity. Chemical and biomolecular engineer, Sibani Lisa Biswal, said: “Maximum capacity puts a lot of stress on the material, so this is a strategy to get capacity without the same degree of stress. One thousand milliamp hours per gram is still a big jump.” The team, led by postdoctoral fellow Anulekha Haridas, tested the concept of pairing the porous, high capacity silicon anodes with high voltage nickel manganese cobalt oxide cathodes. The full cell lithium-ion batteries demonstrated their stable cyclability over hundreds of cycles at 1,000mAh/g. Some of the cathodes were given a 3nm layer of alumina, applied using atomic layer deposition. The researchers found that the alumina coating protected the cathode from breaking down in the presence of hydrofluoric acid (which forms if even minuscule amounts of water invade the liquid electrolyte). Testing showed that the alumina also accelerated the battery’s charging speed. Ms Haridas explained: “There appears to be extensive trapping as a result of the fast lithium transport through alumina.” The researchers already knew of possible ways in which silicon anodes trap lithium, rendering it unavailable to power devices, but this is believed to be the first report of the alumina absorbing lithium to saturation point. Once saturated, the alumina layer itself becomes a catalyst for fast transport to and from the cathode. Concluding, MsHaridas said: “This lithium-trappingmechanism effectively protects the cathode by helping maintain a stable capacity and energy density for the full cells”.

Researchers from the French National Institute of Health and Medical Research have developed a yarn using human skin cells. In their paper, published in the journal Acta Biomaterialia , the group described the process and the potential applications for a material that can be woven into human textiles. Medical textiles are used to heal skin and other body parts, or to replace parts of organs, but not all patients have the same reactions to all textiles because the materials are often treated as foreign agents by the immune system and rejected. The new material, created from human fibroblasts (cells that assist with the production of collagen) will be acceptable to the body because it consists of natural human cells, possibly using the patient’s own cells. The researchers have already created textiles for a variety of applications. Skin cell fibroblasts are grown into sheets of material, and the sheets are “styled” into desired shapes, or cut into strings to use as sutures. These strings could also be twisted or knotted, or used like yarn. A notable advantage of the new technique is that it does not require the use of scaffolds to create organ parts, they are simply fashioned in a way similar to knitting; the team suggest it could be used to create pouches, valves or tubes. The new material has been tested on animals – researchers created a tube from the yarn and grafted it onto an artery in a test sheep, and have also used it to suture wounds – and are ready to start testing it with human patients. In application, the researchers claim the material functions as well as other products currently in use. Strengthening 3D-printed titanium A team of engineers at the Royal Melbourne Institute of Technology (RMIT) has developed a method to print titanium- copper alloys, a lightweight material used in many types of aerospace and medical device applications. “Current titanium alloys used in additive manufacturing often cool and bond together in column-shaped crystals during the printing process, making them prone to cracking or distortion,” said Mark Easton, a professor of manufacturing, materials and mechatronics at RMIT. “And, unlike aluminium or other commonly used metals, there is no commercial grain refiner for titanium that manufacturers can use to effectively refine the microstructure to avoid these issues. “[Our process features a] fully equiaxed grain structure. This means the crystal grains grow equally, in all directions, to form a strong bond, instead of in columns which can lead to weak points liable to cracking. Alloys with this microstructure can withstand much higher forces and will be much less

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MAY 2020