The avalanche effect: a new understanding of lithium ion movement in graphite

Researchers at the Cavendish Laboartory have used a new optical technique to show that in the early stages of charging lithium ions enter the graphite lattice in sudden, localised, intermittent jumps – like microscopic “avalanches”.

This discovery, published in Nature, offers a vital insight into lithium ion movement – a key to further improvements in developing safe, high energy density, fast-charging batteries.

In rechargeable batteries, lithium ions pass back and forth between electrodes – from negative to positive during discharge, and vice versa during charging. The electrodes are essentially a composite sponge containing millions of active particles with a layered structure that lithium ions shuffle into and out of (known as intercalation).

Material scientists have been interested in what happens to these materials as they fill with lithium. Do they fill continuously, or do they fill under specific symmetries (or phases)? And if so, how do they transition from one phase to another?

This phase transition behaviour fundamentally determines key properties: how fast batteries charge, how much energy can be stored, and how many cycles will the battery usefully last.

Up until now the lithium-ion-filling behaviour of the graphite anode has been treated as settled textbook science. Standard models have long assumed that during early charging, lithium ions insert smoothly and continuously between graphite sheets. The new study challenges this narrative.

The team used a high-speed optical technique developed by Illumion, a spin out of the Cavendish Laboratory, to look at a single active particle of graphite.

Researchers observed something entirely unexpected: instead of smooth, continuous filling, lithium ions enter the graphite lattice in sudden, localised, intermittent jumps – like microscopic “avalanches”. Because conventional techniques usually look at the whole battery (containing millions of particles) at much slower speeds, this phenomenon was previously missed.

This observation builds a bridge to entirely different fields of physics.

To explain the chaotic, step-like behaviour, researchers looked beyond standard electrochemistry to statistical mechanics – specifically, how structural disorder affects non-equilibrium phase transitions. What they saw is well known outside of battery science.

“When you slowly drive an imperfect, disordered system, energy builds up and releases in sudden bursts,” said Jiho Han, first author of the paper and PhD student in Akshay Rao’s group at the Cavendish Laboratory. “It’s a universal phenomenon across nature: it happens over vast distances during earthquakes as tectonic plates slowly grind together, in magnetic materials under a changing field, or when liquid squeezes into a disordered network. Yet, this crackling behaviour was never expected in ionic systems like batteries, where filling was thought to be governed purely by smooth reaction rates and ion diffusion.”

The discovery redefines how researchers view the intercalation of lithium ions in graphite. By proving that microscopic structural disorder dictates how the graphite takes in lithium during early charging, researchers can begin building models that account for real-world imperfections and charging behaviour.

By bridging battery engineering with fundamental physics the team has developed a vital insight needed to decode ion movement – a key to further improvements in developing safe, high energy density, fast-charging batteries.

This research was partly funded by the Faraday Institution, part of  the LEAP Project.

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Reference: 

Han, J., Phillips, G.S., Merryweather, A.J. et al. ‘Avalanche-like intercalation and intraparticle correlations in graphite.’ Nature (2026). DOI: 10.1038/s41586-026-10862-4

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Adapted from a Faraday Institution’s article.