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The search for a sustainable EV battery has taken the iconic automaker Mercedes-Benz in some strange directions. The latest news involves a new method for extracting hard carbon from rice hulls, leading to new EV battery anodes that outperform conventional — and less sustainable — anodes made from conventional graphite.
The Sustainable EV Battery Of The Future, From Lignin
Rice hulls are the latest twist in the race to decarbonize the EV battery supply chain. Conventional lithium-ion batteries rely on graphite, which can be mined from the earth or synthesized from fossil fuels. Either way, much of the US graphite supply comes from overseas. Both versions also involve carbon emissions among other environmental impacts, which presents a challenges for automakers seeking to claim the #1 sustainable brand for themselves.
Last year researchers at Northwestern University released the results of a first-of-its-kind, soup-to-nuts analysis of graphite usage in the US and noted a good deal of waste, much of it involving refractories and foundries with a lesser amount from EV battery makers. “Recycling more graphite and producing graphite from lignin would favorably influence today’s supply chain,” the research team concluded.
From a sustainability perspective the lignin pathway is particularly promising because it can help divert agricultural waste from landfills and into a more useful second life, replacing fossil-sourced synthetic graphite.
From a science perspective, though, the biomass pathway is challenging. The conventional method is to extract carbon from burned-up biomass, but that yields a disordered from of carbon, not graphite. Exposing biomass to extremely high heat yields a higher-quality carbon product, but at the price of increased carbon emissions.
The Rice Hull Solution For The Sustainable EV Battery Of The Future
The new rice hull research project was conducted by a research team at the University of Michigan, with primary funding from the National Science Foundation along with the Research & Development North America branch of Mercedes-Benz.
The University of Michigan points out that producing EV battery-grade graphite from biomass generally involves five to 10 tons of carbon dioxide emissions per ton of graphite, based on a high-heat scenario.
That doesn’t mean the biomass-to-graphite pathway is a lost cause, sustainably speaking. Instead, the researchers advocate for selecting specific types of biomass that are more amenable to graphite production. They zeroed in on rice hulls partly due to the availability of a domestic supply chain for EV battery makers, with US producers generating about 20 billion pounds of rice annually.
The team also drew on on their previous research, which involved creating a method for extracting silica from rice hull ash. The silica can be repurposed as silicon for solar cells and other products, while the remaining ash is 60-70% carbon.
“The leftover carbon was thought to be shapeless and disorganized, a material called amorphous carbon,” the school recounts. Upon further analysis deploying specialized spectroscopy equipment, the researchers determined that nanoscale “islands” of graphite were disbursed within the matrix. Instead of an amorphous mess, they found an ordered form of carbon called hard carbon.
As for how that came to be, it has something to do with the unique characteristics of rice hulls. “Hard carbon can be produced by combustion in this case because as you burn away the carbon of rice hulls, you create a shell of silica around the remaining carbon and it bakes it like a pie,” explains U-M professor Richard Laine, the corresponding author of the study.
Rice Hulls Outperform Graphite In Lithium-Ion Batteries
The big question is whether or not hard carbon made from rice hulls can match the performance of conventional graphite when deployed in the anode of an EV battery. The researchers arrived at the answer no, rice hulls don’t match the performance. They exceed it.
“When testing the electrochemical properties of hard carbon obtained from rice hull ash, it outperformed both commercial hard carbon and graphite as the anode of a lithium-ion battery,” U-M explains.
As described by the school, one gram of conventional graphite in an EV battery can accept about 370 milliampere-hours (mAh). Conventional hard carbon does much better, at about 500 mAh, but the hard carbon produced from rice hull ash outperformed both by a wide margin, at 700 mAh.
Next Steps For A Sustainable EV Battery
Of course, a more sustainable EV battery is the one that goes into a bus or some other form of alternative transportation, not an individual car. However, car culture will not go away any time soon. Replacing conventional graphite and hard carbon with bio-based sources can help alleviate local waste management issues in addition to reducing EV battery supply chain impacts.
Another example of the bio-based approach comes from the Karlsruhe Institute of Technology in Germany, which participated in the U-M research. Back in 2016 the school published the results of a study deploying Germany’s copious amount of agricultural waste from apple orchards to produce a bio-based carbon material for a sodium-ion EV battery.
Hold onto your hats. While researchers are still studying the apple waste angle, the Malaysian startup Graphjet is going after the massive amount of palm kernel shells disposed of by the palm oil industry each year.
Last month the company announced that its factory in Malaysia was up and running, aiming to produce 3,000 metric tons of graphite yearly from up to 9,000 metric tons of palm kernel shells.
“Additionally, the Company plans to produce hard carbon at the facility to provide feedstock for its planned green graphite facility in Nevada,” Graphjet explained in a press release dated November 19.
How’s that again? It looks like we have some catching up to do. Graphjet announced the Nevada venture on April 8 of this year, billing it as a “first-of-its-kind” facility for the US.
Once up and running in 2026, the new US facility will process hard carbon from the Malaysian operation, equivalent to 30,000 metric tons of palm kernel yearly. Graphjet expects the US facility to produce up to 10,000 metric tons of battery-grade graphite from the bio-sourced hard carbon.
As for why Nevada, that’s easy. “Nevada is a strategic location for Graphjet as it is located in close proximity to a large quantity of battery manufacturers and automotive OEMs, which will require a significant amount of graphite for future EV battery production,” Graphjet observes.
The company also offers up some hard numbers in terms of carbon emissions. According to their calculations, their bio-based graphite operation involves far lower carbon dioxide emissions (2.95 C02 emissions per KG of graphite) than natural graphite from Canada (9.2. C02 emissions per KG) and synthetic graphite produced in China (17 C02 emissions per KG).
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Photo: The humble rice hull could provide EV battery makers with a more sustainable, bio-based graphite supply chain that outperforms conventional graphite, too (courtesy of US Department of Agriculture).
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