Researchers are trying to improve battery performance in low-temperature environments

2024-01-23

By using rechargeable battery technology to store energy, our digital lifestyle is now full of power. On the one hand, renewable energy can also be integrated into the grid. However, the functionality of batteries in cold conditions remains a challenge, prompting research to improve their low-temperature performance. Water based batteries (in liquid solutions) have a better discharge rate at low temperatures (measuring the energy released per unit time) than non-aqueous batteries.

A new study by engineers from the University of Hong Kong was recently published in the journal Nanoresearch Energy, proposing the optimal design elements for aqueous electrolytes used in low-temperature aqueous solution batteries. This study examined the physical and chemical properties of water electrolytes (determining their performance in batteries) based on several indicators: phase diagram, ion diffusion rate, and kinetics of redox reactions.

The main challenges of low-temperature aqueous solution batteries are electrolyte freezing, slow ion diffusion, and delayed redox kinetics (electron transfer process) as a result. These parameters are closely related to the physical and chemical properties of the low-temperature water-based electrolyte used in the battery.

Therefore, in order to improve the performance of batteries under cold conditions, it is necessary to understand the reaction of electrolytes to cold conditions (-50 ° C to -95 ° C/-58 ° F to -139 ° F). The research author and associate professor Yi Chun Lu said, "In order to obtain high-performance low-temperature aqueous solution batteries (LT-ABs), it is very important to study the physical and chemical properties of aqueous electrolyte with temperature changes to guide the design of low-temperature aqueous solution electrolytes (LT-AEs)."

The figure shows the design strategy of the water electrolyte, including antifreeze thermodynamics, ion diffusion kinetics, and interfacial redox kinetics.

Researchers compared various LT-AE technologies used for energy storage, including Li+/Na+/K+/H+/Zn2+- batteries, supercapacitors, and flow battery technologies. This study collated the information about the performance of various LT-AEs in many other reports, such as the antifreeze hydrogel electrolyte used for Zn/MnO2 water battery; And ethylene glycol (EG) - H2O mixed electrolyte for Zn metal batteries.

They systematically studied the equilibrium and non-equilibrium phase diagrams of these reported LT-AEs to understand their antifreeze mechanisms. The phase diagram shows the changes of the electrolyte phase at different temperatures. The study also investigated the relationship between the conductivity of LT-AEs and temperature, electrolyte concentration, and charge carrier.

Research author Lu predicts that "an ideal antifreeze electrolyte should not only exhibit low freezing point temperature Tm, but also have strong undercooling ability," meaning that the liquid electrolyte medium should remain liquid even below freezing point temperature, thereby achieving ion transport at ultra-low temperatures.

The research authors found that most LT-AEs that enable batteries to operate at ultra-low temperatures exhibit low freezing points and strong undercooling capabilities. In addition, the strong undercooling ability can be achieved by increasing the minimum crystallization time t and increasing the ratio value of the glass transition temperature and freezing temperature (Tg/Tm) of the electrolyte.

By reducing the energy required for ion transfer, adjusting the electrolyte concentration, and selecting certain charge carriers that can promote rapid redox reaction rates, the reported charge conductivity of LT-AE for batteries can be improved. Lu said, "Reducing diffusion activation energy, optimizing electrolyte concentration, selecting charge carriers with low hydration radius, and designing synergistic diffusion mechanisms will be effective strategies to improve the ion conductivity of LT-AEs."

In the future, the author hopes to further study the physical and chemical properties of electrolytes that can help improve the performance of low-temperature water batteries. Lu said, "We hope to develop high-performance low-temperature water batteries (LT-ABs) by designing water-based electrolytes with low freezing point temperature, strong undercooling ability, high ion conductivity, and fast interface redox kinetics."

Honda applies for a motorcycle autonomous driving patent to easily balance vehicles