Scientists have discovered that the use of sugar in anode substrate can prevent formation of dendrites in lithium battery, paving the way for it to become next-generation high-energy and -density battery.
Dendrites are formed resulting from uneven deposition of lithium on electrodes of lithium battery, which could cause loss of battery capacity, reduction in charging and discharging efficiency, and short circuit. It is quite similar to whisker formed in electronic components, which appeared, for instance, at welding spots of vacuum tubes, using tin or alloy near pure tin as welding material, which were in popular use during early 20th century.
Ming Tang, assistant professor in material science and nano engineering at Rice University, pointed out that the formation of dendrites in lithium battery is related to compressive stress, similar to the cause for whisker, although knowledge on the appearance compressive stress at the welded layer of lithium battery is still insufficient.
To have better understanding of the problem, researchers simulated compressive stress on the surface of electroplated soft metal, to manifest how lithium dendrites grow. The experiment showed that spreading of lithium on a flat substrate blocked the outreach of lithium, forcing it to beget the form of dendrites.
Lithium's melting point stands at 180.5 Celsius, lower than tin, which is why lithium atoms are more fluid under room temperature and are more likely to move under pressure, enabling formation of dendrites in a matter of several hours or even several minutes.
To address the problem, the research team developed a technique to help curtail the formation of dendrites, featuring the use of sugar. They injected sugar, alongside liquid PDMS, into the substrate and then melted sugar, leaving a 3D porous structure of soft silica gel, just like a collapsible and deformational sponge, which was then covered with a thin copper layer for electronic conduction and filled with lithium for its holes.
In the experiment, formation of dendrites was cut significantly, as the wrinkled substrates following melting of sugar alleviates accumulation of compressive stress inside lithium, enabling the battery to keep 98% coulomb efficiency after 200 times of cycles. The research team will make some adjustment on the battery, in order to attain commercialization of the technology. The paper on the study has been published in the "Nature Energy" journal.
