BETTER BATTERIES

When it comes to batteries, lithium-ion is king. They’re lightweight and very energy dense, meaning they pack more power per weight than other batteries.

But they’re also prone to catching fire if damaged. And if every car went electric or hybrid, there wouldn’t be enough lithium to go around. So researchers are looking at ways to make them safer and replace lithium with more plentiful, cheaper metals.

Different lithium-ion batteries have different compounds at the anode and cathode. Briefly, the lithium-ion battery you might find in your smartphone comprises a positive electrode (anode) made of lithium cobalt oxide and a negative electrode (cathode) of carbon bathed in electrolyte. The electrodes are separated by a thin plastic membrane that selectively lets lithium ions through.

As the battery charges, lithium ions move from the anode through the membrane to the cathode. As it discharges, the ions move back to the anode. Electrons, blocked by the membrane, travel to the anode through an external wire to produce electricity. Sodium is a contender to replace lithium, but because sodium ions are larger and heavier, the batteries aren’t as energy-dense. And while that might rule them out for smartphones, they’re ideal for jobs such as storing solar energy. Calcium, magnesium, aluminium and potassium are also in the running, with each at varying degrees of research, prototyping and commercialisation.

What about safety? Samsung’s notoriously faulty Note 7 batteries caught fire when the separator membrane wore thin or tore and the electrodes touched. This short-circuited the battery, igniting the flammable electrolyte. To this end, materials scientists are exploring non-flammable, solid electrolytes.