Framework developed to guide electrolyte design for batteries

Researchers at Tohoku University in Japan have developed a framework to predict how the structure of solid-state electrolytes can affect the performance of a battery. Solid-state batteries are a safe option to hold energy, but effectively harnessing their structure–performance relationship is a complex barrier to better batteries. Co-corresponding author Hao Li, an associate professor at WPI-AIMR, said developing promising energy storage devices is critical to realising a sustainable future.

“Over the past few decades, many attempts to find ‘beyond lithium’ battery electrolytes have been reported, and, in particular, divalent closo-type complex hydride (CTCH) electrolytes are valuable alternatives to overcome the safety and energy density limitations of lithium-ion technology,” Li said.

A typical battery consists of oppositely charged metal electrodes in a liquid electrolyte. Lithium ions diffuse the positively charged electrode and attach to carbon on the negatively charged electron. The process reverses when energy is used. CTCH electrolytes, according to the researchers, can accelerate the rate at which positive ions diffuse during the process. This increased conductivity is achieved by adding neutral molecules to the CTCH’s structural lattice.

Co-corresponding author Shin-ichi Orimo said neutral molecule-containing CTCHs are a class of promising but highly complicated materials. “The key determinants of their performance as battery electrolytes and their structure–performance relationships have been a big mystery that hampered the exploration of the ionic diffusion mechanism and the design of high-performance batteries,” Orimo said.

To address this challenge, the researchers combined a genetic algorithm, which imitates the process of natural selection to refine a population’s subjects, with computational modelling of how energy functions within a system. With this framework, the researchers found they could predict how adding neutral molecules to a CTCH would affect its performance. Without using any experimental information to set the parameters, the researchers used this strategy to successfully predict structural information and diffusion activation energies. Their predictions compared nearly identically with experimental observations.

“Based on these results, we developed robust structure–performance relationships that can precisely predict the divalent CTCH performance and identify the key factors that affect ionic conductivity. This study paves a new avenue for building a precise structure–performance picture of complex materials starting from near-zero information,” Li said.

Next, the researchers plan to design and screen high-performance and cost-effective electrolytes, as well as apply the framework to better understand other classes of solid-state electrolytes. The research findings were published in the journal Chemistry of Materials.

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