Nano Researchers Grow Ingredients for Faster Lithium-metal Batteries

In a recent study published in Nature Energy, a team of nano researchers from the University of California San Diego found a way to grow single-crystalline seeds that result in dense lithium deposition. This translates to lithium-metal batteries capable of charging faster (about an hour) than their lithium-ion counterparts—overcoming a key technical barrier and paving the way for improved fast charging in electric vehicles and portable electronic devices. 

 

Imaging from a scanning electron microscope (SEM) shows uniform lithium-metal crystals growing on a nanocomposite surface. Image used courtesy of the University of California San Diego

 

The research received funding from the U.S. Department of Energy’s Battery500 Consortium, a program aiming to build batteries with superior performance. The study’s findings challenge the makeup of industry-standard lithium-ion batteries used in most EVs. Depending on the voltage of the EV battery pack and the input voltage of the charger, EVs may take several hours to charge. The quickest method is direct current (DC) fast charging, which can juice up an EV from empty in 20 minutes to an hour, according to the U.S. Department of Transportation. 

Lithium-metal batteries use a lithiophilic surface to achieve dendrite-free lithium deposition at high charge densities. However, this means the batteries must charge slowly to reduce the formation of dendrites, which are non-uniform deposits that can cause short circuits and capacity losses. 

Batteries with lithium-metal anodes can provide around twice the energy density of typical lithium-ion batteries. However, the associated downsides include dendrite growth, volume change, and poor efficiency due to electrolyte reactions, according to the UC San Diego research team behind the study. As such: eliminating those side effects would be a major advancement in unlocking faster battery charging. 

Ping Liu, a UC San Diego nanoengineering professor, said in the university’s press release that the discovery of using nanocomposite surfaces challenges the traditional concept that lithium grows better on lithiophilic surfaces, materials favorable to lithium. Instead, Liu and colleagues used a lithiophobic substrate that provides abundant nucleation sites and fast movement of lithium on the surface. 

 

Countering the Performance Effects of Fast Charging 

Fast charging is characterized by high current densities, which can cause lithium to accumulate and lead to mechanical stress. This results in dendrite growth, followed by short circuits and performance degradation. 

 

This graphic shows the UC San Diego researchers’ process for controlling the nucleation and growth of lithium metal, forming single crystals that result in dense lithium formation. Image used courtesy of the Liu Research Group at UC San Diego

 

To counter these performance effects, the UC San Diego researchers used a lithiophobic surface instead of a lithiophilic one. The surface consisted of a nanocomposite of lithium-fluoride (for rapid lithium transport) and iron (with uniform sites for nucleation) to deposit hexagonal crystals, leading to dense lithium deposition. 

On the surface, lithium crystal seeds formed to grow dense lithium layers that could beat the charging rates of existing processes. The researchers tested it on a cell for over 130 cycles with 80% capacity retention, yielding a 550% improvement over the baseline cells.