The avalanche effect: a new understanding of lithium ion movement in graphite
As part of the Faraday Institution Degradation (now LEAP) project, researchers at the University of Cambridge have used a new optical technique developed by Illumion 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 – is a vital insight into lithium ion movement – a key to further improvements in developing safe, high energy density, fast-charging batteries.
Battery charging and discharging
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.
Developing a refined understanding
The new study challenges this narrative.
The team used a high-speed optical technique developed by Illumion to look at a single active particle of graphite. Illumion is a spin out of the University of Cambridge that was previously supported by the Faraday Institution via an Entrepreneurial Fellowship.
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.
Video taken from an operating battery cell during a charge, from a single ~10 μm wide graphite particle, which highlights lithium moving into the particle in fast, localised bursts of activity (highlighted in blue).
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.
Jiho Han, PhD researcher in Akshay Rao’s group, Cavendish Laboratory, University of Cambridge, describes how:
When you slowly drive an imperfect, disordered system, energy builds up and releases in sudden bursts. 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.”
Unlocking new avenues of research
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.
Jiho Han, a PhD Student at the Cavendish Laboratory, explains his research into how lithium moves into graphite, the material used in most lithium-ion battery negative electrodes.
The Faraday Institution LEAP project has been enabled thanks to funding from the Battery Innovation Programme, through the Department for Business and Trade and delivered by Innovate UK.
Success story published August 2026.