Improving electrodes to make the sea "fishing" lithium more efficiently
Lithium can be extracted from Bolivian sea water. Image source: GETTY IMAGES
With the vigorous development of the electric vehicle industry, the market's demand for lithium continues to grow. This light metal is the key to making high-power rechargeable batteries, but its insufficient reserves have always been a problem. Recently, a study from Stanford University in the United States has taken an important step towards the unlimited supply of lithium resources. Its researchers are trying to extract lithium directly from seawater.
Compared with other battery materials, lithium can store more energy in the same weight unit. Every year, manufacturers of lithium batteries can consume 160,000 tons of raw materials. In the next ten years, this demand will increase by nearly ten times.
The lithium resource in seawater is considerable, and the global ocean contains about 180 billion tons of lithium. The problem is that the concentration of lithium in seawater is very rare, about 0.2 parts per million. Researchers have designed a variety of filters and membranes to specifically extract lithium from seawater. But so far, related technologies have required a large amount of evaporated seawater to increase the concentration of lithium. This method is not cost-effective to account for the occupied land and the time spent.
Some scientists have also tried to put the lithium battery electrode in seawater, and use the negative voltage on the electrode to lift lithium. However, there is still a large amount of sodium in seawater, and a large amount of sodium is often added during the lithium extraction process, and even squeezes out the extraction space of lithium.
In a study published this month by Joule, Stanford University professor Cui Yi team proposed a more targeted method of lithium extraction. They coated a thin layer of titanium dioxide on the electrode. Lithium ions have a smaller volume than sodium ions, so it is easier to pass through the film and enter the electrode.
The team also changed the method of controlling the voltage. They took a cyclical approach: first apply a negative voltage, then temporarily turn off, then apply a positive voltage, and then turn off, so the cycle repeats, can be repeated ten times in a few minutes.
This design is because the voltage change will also affect the lithium ion and sodium ion closer to the electrode. After using electrode materials with higher affinity for lithium, lithium ions will enter the electrode earlier than sodium ions, and will leave the electrode later. After several cycles, lithium can be concentrated in the electrode. In the end, the researchers got a 1:1 ratio of sodium to lithium.
In an interview with Science, Cui Changxu, a chemical engineer at Seoul National University in South Korea, commented on the study, "This technology means that the field has made a substantial progress in research", and pointed out that the technology has recovered lithium resources in used batteries. May also help.
Some scholars also pointed out that compared with mining lithium resources on land, the cost of this method is not low. Some research teams are trying to improve the electrodes, trying to broaden their choices and reduce costs. (Yuan Liu)
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