According to a paper published in the journal Nature Nanotechnology, scientists from Stanford University have successfully created a battery with a lithium anode, something that’s eluded them for decades.
Regardless of type, all batteries have three basic parts: an electrolyte to provide electrons, an anode to discharge the electrons, and a cathode to receive them. The lithium batteries of today are not really lithium batteries; the lithium is only present in the electrolyte, not in the electrode. This is because the lithium ions released during charging expand at the anode and cathode causing the electrodes to break down. In truth, graphite, silicon, and all other anode materials expand during charging, but nowhere near the same degree as lithium, which expands exponentially and causes cracks on the outer surface.
Yi Cui, a professor of Material Science and Engineering and leader of the research team, explains: “Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail. It is very lightweight and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller batteries with more power.”
Realizing a lithium anode will deliver a massive boost in battery efficiency, and play a significant role in meeting the hefty energy demands of electric cars as well as future generations of handheld electronics. A fully implementation of is expected to double or triple smart phone battery life or extend electric vehicle’s driving range to 300 miles.
To finally solve this puzzle once and for all, scientists built a 20 nanometer thick protective layer of interconnected amorphous carbon domes, called nanospheres, on top of lithium anode. The nanospheres are honeycomb-shaped to create a flexible, uniform, and non-reactive film that prevents the electrodes from cracking and reduces the likelihood of overheating, another issue associated to lithium batteries.
“The ideal protective layer for a lithium metal anode needs to be chemically stable to protect against the chemical reactions with the electrolyte and mechanically strong to withstand the expansion of the lithium during charge,” Cui said.
However, there is one drawback: to be commercially viable, the battery must have a coulombic efficiency – a ratio of the amount of lithium can be extracted from the anode when the battery is in use versus the amount replaced during charging – of 99.9 percent or more. The best results achieved by past lithium electrode battery experiments yielded 96 percent efficiency, which dropped to less than 50 percent in 100 cycles. The Stanford team’s lithium electrode retained 99 percent efficiency after 150 cycles.
“The difference between 99 percent and 96 percent, in battery terms, is huge. So, while we're not quite to that 99.9 percent threshold, where we need to be, we're close and this is a significant improvement over any previous design,” Cui said. Regardless, they are on the cusp of something revolutionary. A bit more engineering and a new generation of rechargeable batteries will be upon us.
Via Phys.org
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