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LuxeSci Show Notes: S1E8: Garnets

Hello again!  Welcome back to the LuxeSci Podcast, a podcast to re-ignite your wonder by exploring the intersection of science and luxury. I’m Dr. Lex, PhD, infectious disease expert, podcast host and lover of a good list, seriously, bring me all the lists. I heard from some of you that you enjoyed last week’s guest hosts so we’re going to continue to experiment with format a bit.  I’m joined again today by Dimos, audio engineer, electrical engineer and lover of a good conversation.  I have to admit to a bit of secret agenda in inviting Dimos back.  Not only is he a good co-host, but also has a little bit of a background in today’s topic.  You’ll see why in a minute.  So about the lists….not only am I a consummate To Do list maker, I love a good list of categories; anniversary presents by year, all those good things.  One of my favorite lists is birthstones so I decided to do a series on birthstones.  When there’s enough scientific background, I’ll do an episode on a birthstone.  Since its January, we’re going to start with garnets.  Now I know that rubies are supposedly the quintessential red gemstone but I have to admit to liking the deep red of garnets better, which is probably a good things since rubies are extremely expensive.


Background:

  • First - birthstone lists

  • There is not a clear history of birthstone lists.  There seems to be links back to eight and ninth century religious practices of associating a particular stone with one of the 12 apostles and wearing one a month.  

  • The custom of wearing a single birthstone is either from Germany in the 1560s or Poland in the 18th century

  • In 1912, the National Association of Jewelers in the US met and officially adopted a list. 

  • The list was updated in 1952, 2002 and 2016

  • Interestingly, in other (non-WEstern) cultures - birthstones aren’t associated with birth month but with celestial bodies.  A good example is from Hinduism where there are nine gemstones associted with different celestial bodies and when a baby is born and their astrological chart is calculated, stones are recommended to be worn to ward off potential problems.

  • So in the US standard birthstone list - the birthstone for January is garnet

  • Garnet

  • So we usually associate garnet with red color but garnet are actually a group of closely related minerals that can be found in almost any color

  • The group all have the same crystal structure but vary in chemical composition - hence the different colors

  • Garnets are nesosilicates  and are most often found in the dodecahedral crystal habit - this means that they are silicate materials  (Silicates make up approximately 90% of earth’s crust) that have a 12-sided crystal shape (though they can be 7 or 6-sided as well)

  • Garnets are most commonly found in metamorphic rock.  Interestingly, because the crystal structure of garnet is stable at high pressure and temperatures, they can be used to record pressures and temperatures at which rocks metamorphosis and used as geobarometers/thermometers to measure the history of metamorphic and igneous rocks.  Nature’s science tools!

  • Garnets have been prevalent throughout history for adornment. They were entombed with ancient Egyptian pharaohs, used for signet rings in ancient Rome and were favored by the clergy and nobility during the Middle Ages.


  • So what about the science (aside from the geothermometer coolness)? And this is also why I wanted to have my electrical engineer hubby here.  Garnets can be used in the next generation of batteries!

  • Why is this important - i don’t think most of us pay attention to the batteries in all our devices (at least not until they need to be charged) but the increased demands we’re putting on electric devices and the advent of an electric car boom means we need batteries that have greater capacity, higher performance and faster charging. 

  • According to an article in the Omega journal from the American Chemical Society by Verduzco et al, lithium-ion batteries are the most advanced rechargeable batteries on the market.  

  • So lithium-ion batteries use liquid electrolytes(you know, like in Gatorade) to facilitate the transfer of lithium ions from the anode (-) to the cathode (+) to power our devices.  Lithium as an element is small so that means these batteries can still pack a punch at a small size

  • While these batteries are ubiquitous, there are some disadvantages that make optimization ideal

  • Flammable liquid electrolytes mean toxicity flammability and leakage for manufacturers and end users

  • There are still limits to how much power a lithium-ion battery can achieve based on the liquid electrolyte’s chemical properties

  • Fun fact - the electrolyte layer is what allows the better to store energy when electricity is not being used 

  • So scientists (including Dr Verduzco) are looking at using solid-state electrolytes to improve the lithium-ion battery performance and their safety profiles

  • In solid-state batteries, the electrolytes are solid materials as opposed to the liquid materials currently used.  Solid state electrolytes are not as toxic of flammable and also don’t have the leakage issues of the liquid-state batteries. 

  • However - there is still some optimization to be done before solid-state batteries can completely take over as the preeminent battery technology.  These include:

  • Limited ionic conductivity (the ability to support movement of ions to make the battery work)

  • Formation of dendritic structures

  • Delamination at the anode and cathode electrode interfaces- essentially degradation of the connections at the ends of the batteries

  • And this is where the garnet comes in. For me, it was hard to visualize how a crystal that I usually see in jewelry could be used inside a battery, especially the small lithium ones.  But it turns out you can process garnet into a fine powder and use various methods to incorporate it into the solid-state electrolytes.  The choice of garnet is because it has good ionic conductivity, good chemical stability with Li (so nothing is blowing up) and a wide electrochemical potential window

  • So what are researchers doing to try and optimize these batteries?

  • Quoc Nguyen et al published their research in the journal Frontiers in Chemistry in 2021 looking at a garnet solid polymer electrolyte to stabilize the solid-state batteries

  • They used a cubic garnet oxide electrolyte along with a polymer electrolyte with an ionic liquid in the battery.  

  • This particular mixture used in the battery was tested to see if lithium dendrite formation happens, monitored for energy output and longevity.  

  • The team found that lithium dendrite formation was lessened with this particular combination for the electrolytes and that the resulting batteries were stable for long cycles at high temperatures and compatible with fast charging systems

  • Summary

  • The battery needs of our evolving technology keep growing in terms of both amount of power stored and transferred and the ability to charge quickly

  • The EV market alone is expected to increase rapidly from about $2B in 2018 to $118B in 2025

  • Energy density and safety of LIB has to be increased and their cost has to be decreased to meet this demand

  • The current top-shelf lithium ion batteries have some major downfalls, including being flammable and toxic and prone to leaking

  • Solid-state batteries (that use solid electrolytes as opposed to liquid electrolytes to transfer ions across the battery = power) are the up-and-coming technology that tries to optimize battery performance while removing some of the risks of lithium ion batteries

  • Garnets are a key component to these solid-state electrolytes due to their stable interface with Lithium and also high ionic conductivity

  • Question to Dimos - how would improved battery technology help with renewable energy, such as solar power?


Glossary:

  • Neosilicates

  • Dodecahedral

  • Electrolyte

  • Ionic conductivity

  • Dendrites 


  • If you’re keeping tabs on our cocktail party conversation pieces, you can now add the super fascinating fact that garnets are being used in the latest and greatest battery technology to facilitate a greener future for the planet.  Or maybe say to someone with an amazing garnet cocktail ring “My that ring has so great ionic conductivity”. That’s actually two fun party facts in one, a scientific one and an environmental one.  


I hope you’ve enjoyed this little venture into battery technology with me and I hope you never look at a garnet the same way again.  I know I never will.  Thanks for listening to this episode of LuxeSci.  A very special thank you to my audio engineer and co-host, Dimos.  Our theme music is Harlequin Moon by Burdy. If you have a correction, comment or suggestion for a topic, you can reach me at: drlex@luxesci.com.  We’re on Twitter and Instagram at luxescipod and our website is luxesci.podcastpage.io.  If you like us, please subscribe.   Please also leave us a review where ever you listen to podcasts.  See you again in 2 weeks!







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