Transient electronics—which work for a short period of time and then undergo triggered self-destruction—have a wide range of potential applications, from military and homeland security to biomedical devices. However, the transient electronic devices produced thus far all have external (non-transient) power sources, which ultimately limit their use.

Now researchers at Iowa State University (ISU) and Ames National Laboratory have now developed a 2.53-V Li-ion battery that dissolves and disperses in 30 minutes when dropped in water. The proof-of-concept battery, described recently in the Journal of Polymer Science Part B: Polymer Physics, can power a desktop calculator for only 15 minutes, but more advanced fabrication techniques will improve the efficiency and performance of the cells, researchers say.

Unlike with previous transient batteries that scientists have produced, “the voltage that we were able to achieve is comparable to commercial, conventional batteries,” says study lead investigator Reza Montazami, an ISU mechanical engineer and Ames National Laboratory research associate. Furthermore, whereas other devices only exhibit chemical transiency, the new batteries have a unique physical–chemical hybrid transiency (chemical dissolution of soluble materials combined with physical dispersion of insoluble materials). “[This approach] can open up many doors.”

Transient batteries to date have all been based on technologies other than Li-ion, which is well-established and has been studied for decades. In 2008, for example, researchers fabricated swallowable 0.42-V batteries from Zn and Pt electrodes and a ceramic porous separator, while another group in 2013 created edible 1.06-V sodium batteries based on melanin electrodes. Compared with conventional batteries, however, these and other transient batteries have several shortcomings, including low potential, current, stability, and shelf-life—in part due to not being based on Li-ion technology.

“Commercial batteries based on Li-ion are optimized to have a relatively high voltage,” Montazami says. “Any other chemistry is not optimum.” However, Li-ion batteries are not transient and require their chemistry to be modified to become so. “The main challenge is to keep the desired properties and at the same time modify the system such that it can disintegrate.”

The new Li-ion transient batteries are comprised of an 8-layer system that has the same main components as its conventional cousins, including a cathode, anode, electrolyte, and electrolyte separator. “But in our case we have [an] extra layer of a polymer that acts as a casing and reacts to a solvent,” Montazami says. Although the components are the same, the structure is different. Montazami and his colleagues also had to modify the active material that goes on the electrodes.

The team used polyvinyl alcohol (PVA) and PVA composites for the binder, substrate, and casing materials; LiCoO₂ and Li₄Ti₅O₁₂ for the cathode and anode active materials, respectively; a short-fiber cellulose-based tissue as a separator and electrolyte holder; a LiPF₆-based material for the electrolyte; and carbon black and silver paint for current leads. They fabricated single-cell batteries—just 1 mm thick, 6 mm long, and 5 mm wide—through a process involving the dissolution of materials that are then spray coated layer by layer onto a PVA substrate.

When exposed to water, the PVA swells, creating a force that cracks and breaks the electrodes into small pieces. The substrate dissolves and resorbs into the water, followed by the PVA binder and remaining nanosized pieces of the active materials, which disperse in the liquid. The team found that most of the battery either dissolved or dispersed within about 30 minutes, compared with the hours to days required by previous transient batteries.

“The results have a huge potential in military and security applications,” says Huanyu Cheng, a materials scientist at the Pennsylvania State University, who was not involved in the study. “In addition, the idea to introduce physical or mechanical deformation may lead to other interesting strategies for transient devices.” But Cheng cautions that the current version of the battery should not be used in biomedicine because some components are not biodegradable or bioresorbable. “Another important issue to consider is the encapsulation strategy that is typically used to provide a timeframe of stable operation before the device starts to dissolve,” he says.

Montazami and his colleagues are now trying to better understand and control the battery’s physical transiency, looking in particular into how cracks propagate in the electrodes when the PVA swells. This information could help them design transient batteries with high energy densities that retain fast transiency. “Since this proof-of-concept worked, we can make transient devices that are comparable to conventional devices,” Montazami says.

Read the article in Journal of Polymer Science Part B: Polymer Physics.