An article appearing on June 24, 2022, in Scientific American describes the nontoxic food coating as an important contributor in the fight to reduce plastic pollution. Win Cowger, Environmental Scientist at the Moore Institute for Plastic Pollution Research is quoted stating, “we can see globally that food packaging is the most abundant plastic material in the environment.” And although antimicrobial pullulan fibre (APF) cannot be used with every type of fruit and vegetable (I was having trouble visualizing it with grapes), it can certainly cover a wide range of produce.

The researchers note their reason for using APF which is a polymer fibre. They note that “fibrous materials are an attractive alternative to films for producing antimicrobial food packaging systems because their high surface-to-volume ratios allow for more efficient release of antimicrobial agents.” 

The APF is electrospun using a rotary jet spinning system (FRJS) with water as the only solvent. Pullulan fibre occurs naturally. It is an extracellular polysaccharide that is considered safe by the U.S. Food and Drug Administration. And as you can see from the two avocados pictured above, APF provides a uniform protective coating making the avocado on the right look a bit like a Monarch Butterfly chrysalis.

The FRJS applies the APF using a nozzle spray that focuses a stream on the target fruit or vegetable. It can be layered to produce the coating you see in the picture. The researchers added a green dye to the APF to make it visible so that you can tell the difference between coated and uncoated fruits and vegetables. Applying it took 2 to 4 minutes. Rinsing it off took a few seconds.

The antimicrobial agents integrated into the APF solution include tiny amounts of thyme oil, citric acid and nisin, the latter an antibacterial peptide produced by bacteria commonly used in food preservation. None of these antimicrobials altered the characteristics of the APF coating or negatively impacted the preserved avocado.

The researchers looked at changes in colour, firmness and pH levels externally and internally. An avocado changes colour rapidly as it ripens. The changes occur both externally and internally. The APF-coated produce, when compared to uncoated avocados, displayed less colour change and lighter acidity (pH). The researchers believed the small quantity of citric acid in the APF may have had something to do with the changes to pH.

The researchers exposed the test avocados for up to 24 hours to E. coli, Listeria, and Aspergillus fumigatus, the latter a fungal pathogen. They compared the coated with uncoated produce over a week. Results showed that the APF coating reduced spoiled produce from 90 to 50% after a week and retained most of their weight unlike the uncoated produce.

In their conclusions, the researchers stated, “The water-based synthesis process, the edible and washable nature of pullulan, and high-throughput fibre technology combine to present a promising method to package perishable food products to enhance food safety and quality while reducing food waste.” 

And then there are these other major added benefits: reducing the number of food poisoning cases currently at 600 million, the 420,000 deaths, and the $17.6 billion in the U.S. alone annually in spoilage.

Lithium-ion batteries today dominate the electric vehicle (EV) industry. But the energy density and durability of the technology have led to range and ownership anxiety on the part of potential purchasers of EVs. A battery with greater density, lighter in weight, and more durable in terms of discharge-recharge cycles would be the breakthrough the planet needs to ween ourselves off the internal combustion engine and the greenhouse gas contributions this technology contributes to global warming.

The 631.1-watt-hours per kilogram (Wh/kg) measure achieved by this battery, and its ability to retain 82% capacity after 10,000 discharge-recharge cycles leaves lithium-ion battery packs in the dust. It means EVs equipped with these batteries will easily match the durability of gasoline and diesel-powered vehicles which on average is between 10 and 15 years.

In an interview by Anthony Cuthbertson of The Independent, Li is quoted stating, “This….design shows that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries. And the flexibility and versatility of our multilayer design makes it potentially compatible with mass production procedures in the battery industry.”

Current lithium-ion battery packs produce around 250 Wh/kg. Hydrogen fuel cells in comparison produce 530 Wh/kg. Lithium-ion battery packs on average can be discharged and recharged about 900 times before the upper capacity begins to degrade. Even so, current lithium-ion batteries come with 8-year warranties or 160,000 kilometres (100,000 miles) drive limits which probably means if you currently own an EV, at some point that warranty is going to come into play requiring a new battery pack.

So the performance demonstrated by this Harvard team’s lithium-metal battery at 631.1 Wh/kg and 10,000 discharge and recharge cycles is indeed impressive. And one other thing, this new battery fully recharges in between 10 and 20 minutes. That too is an impressive performance improvement.

The secret to the design of the Harvard battery is an innovative multilayer self-healing assembly which deals with degradation common to lithium-ion battery technology. That degradation you may have experienced when your smartphone starts to overheat. That won’t happen with the lithium-metal solid-state technology design which can be compared to a bacon-lettuce-and-tomato (BLT) sandwich as seen in the illustration above.

Can the battery be scaled down for use where lithium-ion is found today? Think cell phones and A, AA, AAA rechargeables? For the moment, the Harvard invention is at the EV battery-pack scale. But the chemistry and design of lithium-metal should allow the technology to go small sometime in the near future.