Introducing next-gen magnesium-ion batteries

A team of researchers led by Professor Dennis Y. C. Leung from the University of Hong Kong has developed a high-performance quasi-solid-state magnesium-ion (Mg-ion) battery. This design offers a sustainable, safe and high-energy-density alternative to conventional lithium-ion batteries, addressing the limitations of material scarcity and safety concerns.

Recently featured in Science Advances, the Mg-ion battery could provide a new solution, in light of lithium-ion batteries’ limitations. However, in order to develop efficient Mg-ion batteries, the researchers had to overcome the challenge of the narrow electrochemical window in aqueous or water-based systems, and the poor ionic conductivity in non-aqueous systems. The researchers developed a water-in-salt Mg-ion battery with an operating voltage above 2 V. However, it still lags behind non-aqueous counterparts due to the dominance of proton over Mg-ion storage in the cathode.

Sarah Leong, the study’s first author, said hydrogen ions are smaller and lighter compared to metal ions. Because of their size, hydrogen ions can easily get into the battery’s cathode structure. “However, this creates a problem because protons and Mg ions compete for space, which severely limits how much energy the battery can store and how long it can last,” Leong said.

To address this challenge, the researchers developed the quasi-solid-state magnesium-ion battery that uses a polymer-enhanced electrolyte to control the competition between protons and metal ions. The Mg-ion battery features a voltage plateau at 2.4 V and an energy density of 264 W·h kg⁻¹, surpassing the performance of current Mg-ion batteries and almost matching the performance of Li-ion batteries.

The researchers conducted extensive cycling tests on the Mg-ion batteries, and found that even under sub-zero temperatures (-22°C), the Mg-ion battery retained 90% of its capacity after 900 cycles. The battery is also non-flammable and resistant to pressure over 40 atmospheric pressure. This level of performance makes the Mg-ion battery a promising candidate for consumer electronics.

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