From hunger comes ingenuity. And rice husk, a cheaper, more efficient and, above all, less controlled by China alternative to graphite.
In short. A team of researchers at the University of Michigan has discovered that the ash resulting from burning rice husks contains a form of hard carbon that can replace graphite in lithium-ion or sodium-ion batteries. Not as a worse alternative to graphite, but by increasing its storage capacity almost double.
Context. Graphite is used to make the anode of batteries. Its layered structure allows it to house and release lithium ions efficiently. In addition, its electrical conductivity is high, which helps maintain a stable charge transfer, essential in electric cars.
China is one of the main producers of natural graphite and dominates 90% of the supply chain. Especially spheroidal graphite, which is used as the anode material in lithium-ion batteries. Last year, in an escalation of its trade war with the United States, China restricted graphite exports. Countries like South Korea had to turn to graphite from other producers such as Mexico, Mozambique and Tanzania.
The rice husk. What the United States did not expect was to discover a cheap alternative that almost doubles graphite in energy density. Hard carbon extracted from rice husk ash can store more than 700 mAh per gram. In comparison, graphite stores 370 mAh.
Rice is not only grown in China, of course. Rice husk is an abundant agricultural waste in the United States, and therefore a domestic, sustainable and cheap alternative to Chinese-controlled graphite. The team that discovered it has already applied for a patent on the technology.
All advantages. Unlike traditional methods for obtaining hard carbon, which require heating biomass to over 1,200°C without oxygen, the rice husk process takes advantage of a nearly worthless feedstock and avoids the huge emissions associated with conventional graphite production.
The process takes advantage of waste that would otherwise end up in landfills, virtually making it a carbon neutral process. What’s more, high-purity silicon can also be extracted from the 90% silica present in the ash for semiconductors and solar panels. With nine million tons of rice produced annually in the United States, there is plenty of untapped material.
Image | RawPixel, Yu et al.
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