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UvA chemistry master students Peter Jungbacker and Tess van Teijlingen, working at the Research Priority Area Sustainable Chemistry of the Van ‘t Hoff Institute for Molecular Sciences, have studied the pros and cons of the most promising alternative materials for Li-ion batteries. Their findings, which include both the chemical and socio-economic aspects of batteries, have been published as a cover article in the open-access journal 'Materials'.

The study, carried out under the supervision of PhD student Jasper Biemolt and project leaders Dr Ning Yan and Prof. Gadi Rothenberg, is part of the UvA's efforts in the area of electrochemistry, brought together under the umbrella of the new Amsterdam Centre for Electrochemistry (Amcel).

## From flashlights to electric cars

It’s difficult to imagine our lives today without batteries as a portable source of electrical energy. Applications limited a few decades ago to flashlights and portable radios have extended to power mobile phones, personal computers, power tools and even cars, changing the world as we know it and generally improving peoples’ lives across the globe.

Much of this development is thanks to Li-ion battery technology, which has increased the energy density in batteries considerably. The scientific importance of Li-ion batteries is reflected in the awarding of the 2019 Nobel Prize in Chemistry to Stanley Whittingham, John Goodenough and Akira Yoshino. The technology also created a large market: the global lithium-ion battery market was $30 billion in 2017, and is projected to surpass$100 billion by 2025, with an annual growth rate of 17%.

Yet Li-ion batteries also have problems: Today’s batteries are close to the maximum theoretical capacity of 370 mA/g when using the lithium-carbon anode. Other lithium-based batteries that are under development to achieve higher capacities suffer from low cycle stability or experience safety problems - for instance when using pure lithium as an anode with higher energy density. In addition to safety concerns, the already high price of lithium and the depletion of the lithium reserves fuel the search for alternative battery types.

## In search of better batteries

Batteries can be made from many metals, but the most promising alternatives to lithium are sodium, magnesium, zinc and aluminium (see figure). As part of their literature project, master students Peter Jungbacker and Tess van Teijlingen studied the pros and cons of these four alternatives. They categorized the individual metals by the cathode material type, focusing on the energy storage mechanism.

• The study showed that sodium-ion batteries are the closest in technology and chemistry to today’s lithium-ion batteries. Although this lowers the technology transition barrier in the short term, their low specific capacity creates a long-term problem.
• The lower reactivity of magnesium makes pure Mg metal anodes much safer than alkali ones. However, these are still reactive enough to deactivate over time. Alloying magnesium with different metals can solve this problem, and combining this with different cathodes gives good specific capacities, but with a lower voltage.
• Zinc has the lowest theoretical specific capacity, but zinc anodes are so stable that they can be used without alterations. This means that they can be immediately used in stationary systems.
• Finally, aluminium is, in theory, the most promising alternative, with its high specific capacity thanks to its three-electron redox reaction. However, the trade-off between stability and specific capacity is a problem here.

After analyzing each option separately, the team compared them all via a political, economic, socio-cultural and technological (PEST) analysis, covering the parameters of availability, cost, safety, weight, toxicity, performance, and stability (see figure). The review, which is one of the first to analyse both the chemical and socio-economic aspects of batteries, concludes with recommendations for future applications in the mobile and stationary power sectors.

## Original open-access article:

J. Biemolt, P. Jungbacker, T. van Teijlingen, N. Yan and G. Rothenberg: Beyond lithium-based batteries. Materials, 2020, 13, 425.  DOI: 10.3390/ma13020425 (open access)