IISc researchers discover how to make solid-state batteries last longer, charge faster

In a new study published in ‘Nature Materials’ journal, they have identified the root cause of this dendrite formation – the appearance of microscopic voids in one of the electrodes early on. They also show that adding a thin layer of certain metals to the electrolyte surface significantly delays dendrite formation, extending the battery’s life and enabling it to be charged faster.

Conventional lithium-ion batteries which are found in smartphones and laptops contain a liquid electrolyte sandwiched between a positively charged electrode (cathode) made of a transition metal (such as iron and cobalt) oxide and a negatively charged electrode (anode) made of graphite. When the battery is charging and discharging (using up power), lithium ions shuttle between the anode and cathode in opposite directions. The researchers point out that these batteries have a major safety issue as the liquid electrolyte can catch fire at high temperatures. Graphite also stores much less charge than metallic lithium, IISc said in a release.

A promising alternative, therefore, are solid-state batteries, the release said. “Ceramic electrolytes perform even better at higher temperatures, which is especially useful in tropical countries like India. Lithium is also lighter and stores more charge than graphite, which can significantly cut down the battery cost,” it stated.

“Unfortunately, when you add lithium, it forms these filaments that grow into the solid electrolyte, and short out the anode and cathode,” said Naga Phani Aetukuri, assistant professor in the Solid State and Structural Chemistry Unit (SSCU) and corresponding author of the study.

Aetukuri’s PhD student, Vikalp Raj, artificially induced dendrite formation by repeatedly charging hundreds of battery cells, slicing out thin sections of the lithium-electrolyte interface, and peering at them under a scanning electron microscope.

“When they looked closely at these sections, the team realised that something was happening long before the dendrites formed – microscopic voids were developing in the lithium anode during discharge. The team also computed that the currents concentrated at the edges of these microscopic voids were about 10,000 times larger than the average currents across the battery cell, which was likely creating stress on the solid electrolyte and accelerating the dendrite formation,” the IISc statement read.

“This means that now our task to make very good batteries is very simple. All that we need is to ensure that the voids don’t form,” said Aetukuri.

The researchers introduced an ultrathin layer of a refractory metal – a metal that is resistant to heat and wear – between the lithium anode and solid electrolyte. “The refractory metal layer shields the solid electrolyte from the stress and redistributes the current to an extent,” he added.

Aetukuri and his team collaborated with researchers at Carnegie Mellon University in the US, who carried out computational analysis which clearly showed that the refractory metal layer indeed delayed the growth of microscopic lithium voids.

The researchers say that the findings are a critical step forward in realising practical and commercial solid-state batteries. Their strategy can also be extended to other types of batteries that contain metals like sodium, zinc and magnesium.