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Shine ion, crazy diamonds

Drexel researchers have reported that adding nanodiamonds to the electrolyte solution in lithium batteries can prevent the formation of dendrites, the tendril-like deposits of ions that can grow inside a battery over time and cause hazardous malfunctions. (Photo courtesy of Drexel University and Tsinghua University).

Drexel University is using nanodiamond solutions to prevent dendrite formation, creating safer batteries

Researchers at Drexel University in Philadelphia have developed a new electrolyte solution that can also safeguard against short circuiting in li-ion batteries.

Although the key technology driving battery-powered transport (and other consumer goods), the process of charging and discharging li-ion batteries do have an effect on the robustness of the system over time. In particular, the movement of ions can cause the formation tendrils, called dendrites, inside the battery. If these form large enough to puncture the separator in the cell, the battery can short circuit, with disastrous results.

Distinguished University and Bach professor in the Drexel College of Engineering Dr. Yury Gogotsim and his research team from the Department of Materials Science and Engineering sought to investigate ways of preventing this. Together with teams from Tsinghua University in Beijing, and Hauzhong University of Science and Technology in Wuhan, China, they attempted to make lithium anodes more stable and lithium plating more uniform to reduce the growth of dendrites.

They have developed a solution using nanodiamonds — tiny diamond particles 10,000 times smaller than the diameter of a hair. When mixed with the electrolyte solution, these particles are deposited on the electrode and “slide together” to form a smooth surface, reducing the electrochemical deposition of dendrites.

In their paper “Nanodiamonds Suppress Growth of Lithium Dendrites” published in Nature Communications, the team reported that this slows dendrite formation to nil through 100 charge-discharge cycles.

“Battery safety is a key issue for this research,” Gogotsi stated. “Small primary batteries in watches use lithium anodes, but they are only discharged once. When you start charging them again and again, dendrites start growing. There may be several safe cycles, but sooner or later a short-circuit will happen. We want to eliminate or, at least, minimise that possibility.”

 

 

Dendrite formation (illustration and microscopy in left column) occurs in lithium-ion batteries over time and can result in hazardous malfunctions, like short-circuits and fires. Adding nanodiamonds to the electrolyte solution inside the battery imposes order on the lithium ion deposition (right column) so dendrites do not form. Source: Drexel University
Dendrite formation (illustration and microscopy in left column) occurs in lithium-ion batteries over time and can result in hazardous malfunctions, like short-circuits and fires. Adding nanodiamonds to the electrolyte solution inside the battery imposes order on the lithium ion deposition (right column) so dendrites do not form. Source: Drexel University

Tenfold increase

Current battery designs are already configured to use one electrode made of graphite and filled with lithium – rather than just pure lithium – as a means of limiting dendrite formation, but this stores around ten times less energy than pure lithium. Gogotsi’s innovation would therefore enable the use of pure lithium electrodes, and a significant increase in overall cell energy storage.

Initial results show stable charge-discharge cycling for 200 hours. Further research is required to test cells over a longer periods of time and under various conditions and temperatures, to make sure that dendrite formation is prevented.

While clearly not enough for the duties required of EVs – or even phones – there is potential here. Gogotsi, for example, has said that the discovery is only the beginning of a process that could see further electrolyte additives used to produce safer li-ion batteries with greater energy densities.

“It’s potentially game-changing, but it is difficult to be 100 percent certain that dendrites will never grow,” he said. “We anticipate the first use of our proposed technology will be in less critical applications — not in cell phones or car batteries. To ensure safety, additives to electrolytes, such as nanodiamonds, need to be combined with other precautions, such as using non-flammable electrolytes, safer electrode materials and stronger separators.”

Cost may also figure here – diamonds are unlikely to come cheap. However, if anything even resembling a tenfold increase in energy density is possible, battery-makers would do well to explore this avenue.

 

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