Researchers search extensively for cation replacements in 18500 battery

Several studies have reported improvements in battery life and thermal stability based on their findings using simulation-based methods. However, this improvement in turn reduces the battery's discharge capacity, which is the amount of energy the battery can deliver in a single discharge. Therefore, an extensive search for cation replacements that can improve discharge capacity is necessary.

Against this backdrop, a team of scientists led by Professor Ryo Maezono of the Japan Advanced Institute of Science and Technology (JAIST) conducted an extensive screening of different cations to partially replace nickel in nickel-based LIBs and thereby improve the battery's discharge capacity.

The discharge capacity can be determined by the discharge curve, i.e. the change in voltage during charge and discharge, Professor Maezono explained. We used first-principles calculations to evaluate the materials' discharge curves, which in turn determined their discharge capacity. However, these calculations are computationally expensive, so we integrated other methods to narrow down the candidates for cation replacement. To our knowledge, this is the first study to successfully predict cation replacements to increase battery capacity. This groundbreaking research has been published in a recent issue of the Journal of Physical Chemistry C.

One prominent strategy for successfully predicting discharge voltage curves is the Strong Constraint and Appropriate Canonical (SCAN) function. However, this approach is impractical for extensive screening due to the large computational costs involved. Therefore, the team began using relatively inexpensive techniques such as density functional theory and cluster expansion to identify suitable cation replacement candidates, and then applied the SCAN function to the inferred candidates to ensure the reliability and accuracy of voltage predictions.

The screening process showed that the maximum discharge capacity was obtained by partial substitution of nickel with platinum and palladium in nickel-based lithium. These results are consistent with experimental data and validate the proposed method.

While Professor Maezono stressed that more research is needed, he is optimistic about the future of their low-cost screening process. "Our findings show that substituents such as rhenium and osmium provide high discharge capacity. However, these elements are rare and expensive, and putting them into practical use will be challenging. Further research is also needed to achieve the same effect with reduced substitution, multiple element substitution, or anion substitution." "That being said, our new computational technique will accelerate the search for optimal materials to improve battery performance at a lower cost, allowing us to replace most of the existing sources of electricity with carbon-free alternatives."

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