Every time you charge your phone, something remarkable happens inside the battery. Tiny charged particles called ions squeeze through microscopic layers of material, storing energy as they go. When you use your phone, those ions squeeze back out, releasing the energy you need. The whole process works because the material holding those ions stays intact, cycle after cycle, charge after discharge, thousands of times over.

Now imagine that material starts shifting and reshaping itself every time the ions move. Walls that were meant to stay flat begin to slide. Layers that should stack neatly start stacking differently. The whole structure slowly falls apart. That is not a hypothetical problem. It is exactly what happens inside one of the most promising battery materials scientists have been trying to develop for the past decade, and it has been one of the biggest obstacles standing between us and a cleaner, cheaper energy future.

A team of researchers from Italy has now peered inside this problem at the level of individual atoms and finally explained, in precise detail, exactly how and why it happens. Their findings could be the breakthrough that finally makes these batteries practical at scale.

Why We Need a Battery Made From Salt

Most of the batteries powering your devices and electric vehicles today use lithium. Lithium is a remarkable material for batteries. It is light, it moves energy efficiently, and it has powered the portable electronics revolution for three decades.

But there is a problem. Lithium is not particularly abundant. It is concentrated in relatively few places on Earth, mostly in South America, Australia, and a handful of other regions. As demand for electric cars surges and countries worldwide push toward renewable energy systems that require massive energy storage, the pressure on lithium supplies is growing fast. Prices have swung dramatically in recent years, and the prospect of a world dependent on a single scarce mineral for its energy storage needs is making a lot of people understandably nervous.

Sodium offers a compelling alternative. Sodium is the fourth most abundant element on Earth. It is literally in seawater, in table salt, in the ground beneath almost every country on the planet. Sodium batteries would cost less, be easier to source, and could be manufactured virtually anywhere. For large scale energy storage, like storing the electricity generated by solar panels or wind farms for use at night or on calm days, sodium batteries could be transformative.

The problem is that sodium ions are larger than lithium ions. Think of trying to slide a bigger bead through the same necklace. The extra size puts more stress on the material surrounding the ions every time they move, and that stress causes damage. Specifically, it causes the material to undergo what scientists call phase transitions, which is a polite way of saying the structure changes shape in ways it was never meant to.

Layers, Shapes, and the Problem of Unwanted Change

To understand what goes wrong, it helps to picture the inside of a sodium battery cathode, which is the positive electrode where ions are stored during charging. The material looks like a stack of very thin sheets, like the pages of a book but at a scale millions of times smaller than anything you could see.

These sheets are made of manganese and oxygen atoms arranged in a precise geometric pattern. Sodium ions sit in the spaces between the sheets. When the battery charges, sodium ions are pulled out of those spaces. When it discharges, they flow back in.

The key insight is that the shape of those spaces matters enormously. There are two main arrangements that scientists use to describe these structures. In one type, which researchers call P2, the sodium ions sit in prismatic spaces, meaning the surrounding atoms form a shape a little like a triangular prism. This arrangement is excellent for battery performance. It allows ions to move freely and the battery delivers good energy capacity.

But when too many sodium ions are removed during charging, or when the battery is pushed to high voltages, the material does something unwanted. The sheets of manganese and oxygen start to slide sideways relative to each other, like a stack of playing cards being pushed out of alignment. When this happens, the prismatic spaces where sodium used to live transform into a different shape called octahedral spaces, where the surrounding atoms form an eight faced geometric shape instead.

This new structure is called O2 or OP4, depending on how the layers rearrange. Once the material makes this shift, several things go wrong. The volume of the material can change by more than twenty percent, which is an enormous physical stress. The structure becomes less stable and less able to hold sodium ions efficiently. Over repeated charge and discharge cycles, the material degrades. The battery slowly loses capacity and eventually fails.

The question that this research set out to answer was deceptively simple: exactly what happens at the level of individual atoms as this transformation takes place? And can understanding that process help us prevent it?

Watching Atoms Move with a Computer

You cannot literally watch individual atoms rearranging themselves inside a battery. The scales involved are far too small, the speeds far too fast, and the environments far too inaccessible for any physical instrument to observe directly. What scientists can do instead is build mathematical models of the atoms and run simulations on supercomputers.

This is precisely what the Italian research team did, using a powerful approach called density functional theory, which allows scientists to calculate how electrons and atoms will behave based on the laws of quantum mechanics. Think of it as an extraordinarily detailed physics simulator, one that can model what happens inside a crystal when you start removing atoms from it.

But they added something even more sophisticated on top of that. They used a method called the variable cell nudged elastic band approach, which is a technique designed specifically to trace the path that a material takes as it transforms from one structure to another. Rather than simply comparing the starting structure and the ending structure, this method maps out every intermediate step in the journey, revealing the exact sequence of atomic movements involved.

This was the first time this particular method had been applied to this class of battery materials, and the results gave a level of atomic detail that had simply never been available before.

The Moment of Transformation: What Actually Happens

The simulations revealed something fascinating about how the transformation unfolds.

When the manganese and oxygen layers begin to shift, the manganese atoms pass through a brief intermediate state on their way from one arrangement to another. In this fleeting middle state, each manganese atom finds itself surrounded by four oxygen atoms instead of the usual six, arranged in a tetrahedral shape, a pyramid with four triangular faces.

This tetrahedral arrangement is deeply unstable. It requires energy to form, which is why the battery material resists the transition at lower voltages. The amount of energy needed to pass through this tetrahedral intermediate state is essentially the barrier that prevents the unwanted transformation from happening.

But here is the crucial insight: this barrier does not have the same height under all conditions.

At low voltage, when the battery still contains plenty of sodium ions, those ions help shield the oxygen layers from repelling each other. The layers stay calm. The transition is energetically costly and does not occur easily.

At high voltage, when most of the sodium has been removed, that shielding disappears. The oxygen layers start repelling each other more strongly. They want to slide apart. The barrier drops, and the unwanted transformation becomes much easier to trigger.

This explains something that had puzzled battery scientists for years: why these materials seem to work fine at moderate voltages but degrade rapidly when pushed to the highest charge levels. Now there is a precise atomic explanation for it.

The Problem of Stretch and Tilt

The research did not stop at mapping the transition pathways. The team also developed a way to measure and track the distortions happening inside the manganese and oxygen arrangement throughout the charging process.

Manganese atoms in this material exist in two different states. When the battery is partially charged, some manganese atoms have lost three electrons, giving them a particular electronic structure that causes their surrounding bonds to stretch unevenly. This is a well known phenomenon called the Jahn Teller effect, named after two physicists who described it in the 1930s. When a Jahn Teller active atom is present, the six bonds connecting it to its neighbouring oxygen atoms are not all equal length. Some are longer, some are shorter. The resulting stretched, lopsided arrangement creates stress that propagates through the material.

When more sodium is removed and more manganese atoms change their oxidation state, the stretching patterns shift. Some of the stress from unequal bond lengths diminishes. But a different kind of stress emerges: the entire cage like structures surrounding each manganese atom start to tilt and rotate, creating angular distortions rather than length distortions.

The research found that these angular distortions are the real culprit behind the layer sliding transition. Specifically, a type of angular distortion called a shear mode is what triggers the layers to start sliding past each other. When shear distortions accumulate enough, the energy barrier for the sliding transition drops low enough that the layers shift and the structure collapses into the unwanted arrangement.

How Adding Nickel Helps, and Where It Falls Short

The researchers did not study just the pure manganese material. They also examined what happens when nickel atoms are added, replacing some of the manganese in the structure.

This is a strategy that battery scientists have been experimenting with for years. Adding nickel introduces additional electroactive particles that can participate in storing and releasing energy, which allows the battery to operate at higher voltages and deliver more capacity. Nickel addition is already used in many battery formulations for exactly this reason.

The simulations showed that nickel addition does help with one of the two problematic transitions. The energy barrier for the transition that occurs at moderate voltages is significantly higher in the nickel containing material than in the pure manganese version, at 1.70 electron volts compared to 1.24 electron volts. The nickel makes the bonds between the metal atoms and their surrounding oxygen atoms more covalent, meaning the electrons are shared more equally rather than being transferred entirely. This stronger, more stable bonding resists the structural reorganisation.

However, the transition that occurs at very high voltages, when almost all the sodium has been removed, still happens with a relatively low barrier of just 1.04 electron volts even in the nickel containing material. The nickel helps, but does not fully solve the problem. The material still shifts structure at the extreme end of the charge cycle.

This creates a difficult compromise. The higher voltage capability enabled by nickel is precisely what gives the battery its superior energy density. But operating at those voltages is also exactly what triggers the damaging structural change. Restricting the voltage to avoid the transition would solve the structural problem but would sacrifice more than forty percent of the battery capacity. That is not a practical solution.

The Path to a Real Solution

Understanding the precise mechanism of the problem opens up more targeted approaches to solving it.

The research points to two specific things that need to be minimised. First, the bond length distortions caused by Jahn Teller active atoms need to be reduced, because these drive the transition that occurs when sodium re enters the material during discharge. Second, the shear mode angular distortions need to be suppressed, because these are what trigger the layer sliding at high voltages.

Both of these goals can potentially be addressed through careful material design.

One promising approach that the researchers examined involves adding small amounts of lithium alongside nickel in the manganese material. The results were encouraging. The combination of nickel and lithium produced a more stable material, with smaller distortions across the whole charging range and structural behaviour that is much less prone to the unwanted transitions. Even more importantly, the fraction parameter that tracks how dominant shear mode distortions are never reached the critical threshold in this lithium containing material, even at the highest voltages tested.

Why would lithium help, given that lithium itself has supply challenges at larger scales? The key is that a tiny amount of lithium in this context is not acting as the main charge carrier. Instead, the lithium atoms occupy specific positions in the structure and act as stabilisers, strengthening the covalent character of the bonds and inhibiting the shear distortions that trigger layer sliding.

Other approaches also show promise based on these findings. Potassium atoms, for instance, can be placed into the sodium sites of the material. Potassium does not participate in the charging and discharging chemistry, so it stays in position throughout the entire cycle. Its presence in those sites prevents the structural rearrangements that otherwise occur when the sites empty out during charging.

More broadly, the research establishes a simple set of measurable quantities that can be calculated relatively easily on a computer and used to screen new candidate materials before anyone goes to the trouble of synthesising them in a laboratory. These structural distortion metrics act as an early warning system. A material that scores poorly on these metrics is likely to undergo damaging transitions. A material that scores well is worth exploring further.

Why This Matters Beyond the Laboratory

The stakes here are larger than battery chemistry.

The world is in the middle of a rapid transition away from fossil fuels, driven by concerns about climate change and energy security. This transition depends enormously on the availability of affordable, reliable energy storage. Electric vehicles need batteries. Solar and wind farms need batteries to store their intermittent output. Homes and businesses need batteries to manage energy costs.

Lithium is doing much of this work today, but the supply chains for lithium are geographically concentrated, politically sensitive, and increasingly strained by demand. Sodium batteries, if they can be made reliable and efficient enough, would represent a genuinely different kind of option. A battery technology that can be manufactured from one of the most common elements on Earth, sourced from almost anywhere, at a fraction of the raw material cost, would fundamentally change the economics of energy storage.

This research from Italy represents one important piece of that puzzle. By explaining, at the level of individual atoms, exactly why manganese based sodium battery cathodes degrade, and by identifying the precise structural features that control that degradation, it gives materials scientists a new set of tools for designing better alternatives.

The solution probably will not be a single material. It is more likely to be a family of materials, each with a slightly different combination of elements carefully chosen to balance performance and stability. The distortion descriptors developed in this research provide a computational shortcut for exploring that space, allowing hundreds of candidate materials to be evaluated quickly on a computer before narrowing down to the most promising options for physical testing.

The battery that keeps breaking itself may finally have a credible path to being fixed. And if it does, the energy storage systems of the future could look very different from what we use today, more abundant, more affordable, and built on something that has been sitting in your kitchen cupboard all along.

Publication Details: Year of Online Publication: 2025; Journal: ACS Energy Letters; Publisher: American Chemical Society; DOI: https://doi.org/10.1021/acsenergylett.4c03335

Credit and Disclaimer: This article is based on the peer reviewed research paper. The research was conducted at the University of Naples Federico II, Italy. All scientific facts, findings, energy values, and conclusions presented in this article are drawn directly and accurately from the original research. Readers are strongly encouraged to consult the full research paper for complete methodology, data, and scientific detail.