Rechargeable lithium-ion batteries, which are used in everything from electric automobiles to portable devices, and have significantly improved in terms of pricing and capacity, have been the main focus of battery development over the previous several decades. However, despite their critical significance in many key applications, such as implanted medical devices like pacemakers, nonrechargeable batteries have not much improved throughout that period.
Now, MIT researchers have found a technique to increase the energy density of these main, or nonrechargeable, batteries. For a certain quantity of power or energy capacity, they claim it might allow a 50% increase in usable lifespan or a commensurate reduction in size and weight, while simultaneously enhancing safety, with little to no increase in cost.
In a paper published today in the journal Proceedings of the National Academy of Sciences, MIT Kavanaugh Postdoctoral Fellow Haining Gao, graduate student Alejandro Sevilla, associate professor of mechanical engineering Betar Gallant, and four other researchers from MIT and Caltech describe the new findings, which involve replacing the typically inactive battery electrolyte with a material that is active for energy delivery.
A pacemaker or other medical device needs surgery to replace the battery, thus any improvement in battery lifespan might have a substantial effect on the patient’s quality of life, according to Gallant. Because they can provide around three times as much energy for a given size and weight as rechargeable batteries, primary batteries are employed for such crucial applications.
Primary batteries are “essential for situations when charging is not feasible or is impracticable,” according to Gao, because of the difference in capacity. The novel materials function at body temperature, making them appropriate for use in medical implants. Applications could also include sensors in tracking devices for shipments, for example, to ensure that temperature and humidity requirements for food or drug shipments are properly maintained throughout the shipping process, in addition to implantable devices, with further development to make the batteries operate efficiently at cooler temperatures. They may also be used to remotely controlled airborne or undersea vehicles that must be kept ready for deployment over extended periods.
Batteries for pacemakers generally last five to ten years and much less if they must perform high-voltage tasks like defibrillation. However, according to Gao, these batteries’ technology is regarded to be mature, and during the previous 40 years, “there haven’t been any significant advancements in basic cell chemistries.”
The substance that sits between the cathode and anode, the two electrical poles of the battery, and permits charge carriers to travel from one side to the other, is the electrolyte. This new kind of electrolyte is the key to the team’s breakthrough. The scientists discovered that they could combine part of the functions of the cathode and the electrolyte in one molecule, known as a catholyte, using a novel liquid fluorinated substance. According to Gao, this enables the weight of ordinary main batteries to be reduced significantly.
Despite the fact that there are other substances besides this new compound that could theoretically play a similar catholyte role in a high-capacity battery, Gallant explains that those substances have lower inherent voltages that are dissimilar to those of the remaining substances in a typical pacemaker battery, or CFx.
The excess capacity would be wasted due to the voltage mismatch since the battery’s total output cannot be more than the sum of the two electrode materials. However, Gallant notes that with the new substance, “one of the significant advantages of our fluorinated liquids is that their voltage aligns extremely well with that of CFx.”
The liquid electrolyte of a standard CFx battery is crucial because it enables charged particles to move freely between electrodes. However, according to Gao, “those electrolytes are really chemically inactive, so they are essentially dead weight.” This indicates that the electrolyte, which is a major component of the battery, has around 50% inactive material. However, she claims that the quantity of dead weight may be decreased to roughly 20% with the new design using the fluorinated catholyte material.
According to Gallant, the novel cells also provide safety advantages over other types of suggested chemistries since their formula does not involve hazardous and corrosive catholyte elements. Additionally, she adds, early testing has shown that the batteries have a steady shelf life of over a year, a crucial quality for main batteries.
The team hasn’t yet succeeded experimentally in achieving the entire 50% increase in energy density that their calculations projected. According to Gallant, they have shown a 20% increase, which would be a significant improvement for several applications. The researchers can predict the performance of the cell based on the performance of the active material itself, even if the design of the cell has not yet been completely optimised. When scaled up, “we can observe the anticipated cell-level performance can reach roughly 50% greater than the CFx cell,” the researcher notes. The next objective for the team is to experimentally reach that level.
In the next year, Sevilla, a doctorate candidate in the department of mechanical engineering, will concentrate on that task. I was brought into this research to attempt to understand some of the constraints of why we haven’t been able to get the maximum amount of energy density conceivable, he claims. “My job has been to attempt to fill in the knowledge of the underlying reaction’s deficiencies,” the author says.
According to Gao, one key benefit of the new material is that it can be readily incorporated into current battery production processes by just swapping out one material for another. Gao reports that preliminary conversations with manufacturers support this relatively simple swap. She claims that the fundamental raw material, which is now used for other reasons, has already been scaled up for manufacturing and is priced similarly to the raw materials currently used in CFx batteries.
According to her, the price of batteries made from the new material will probably be similar to that of batteries already on the market. The team has already submitted a patent application for the catholyte, and they anticipate that medical uses will probably be the first to be commercialised, maybe with a full-scale prototype available for testing in actual devices in approximately a year.
Future uses of the novel materials might include smart gas or water metres that can be read remotely or devices like EZPass transponders, which would prolong their useful lives, according to the researchers. It may take longer to produce electricity for drone planes or underwater vehicles since they would need more power. Batteries for equipment used in distant locations, such as drilling rigs for oil and gas, as well as sensors lowered into the wells to monitor conditions, might also be employed.
