New charge-trapping insights could help design longer-lasting batteries

Scientists have uncovered a mechanism by which trapped charges called ‘polarons’ alter the structure of silicon nitride when lithium ions enter the material. Using computer models of atomic interactions, they studied how this early, partly irreversible, charge-trapping process could improve battery stability. The results, published as a Hot Paper in the Journal of Materials Chemistry A, can inform the design of more durable conversion-type anodes for batteries. 

A structurally convertible battery material 

In a lithium-ion battery, charged lithium ions move from one end to the other as the battery gets used. Most lithium-ion batteries today are, like pencils, made with graphite. Graphite is used as the anode, which is the negatively charged part of the battery. In these traditional lithium-ion batteries, the material structure of the anode stays fixed, with lithium passing in and out of it when you charge and use your battery. Think of this as a dinner party, with everyone sitting in fixed wooden chairs. 

Now imagine that the dining chairs are made of clay. When everyone sits down for the first time, the structure of their seats changes in response. When they get up, the new structure is left behind, in a shape that is better suited to hold them. Similarly, in conversion-type anodes, the anode material structure actively transforms during the initial charging stage. This provides an anode that is mechanically robust with high lithium capacity over an extended period of time. 

One potential conversion-type anode material is amorphous silicon nitride, which is both lightweight and abundant. To be able to design lithium-ion batteries that use silicon nitride anodes, scientists and engineers need a better understanding of how lithium ions interact with and incorporate into the material. 

Trapping charges for longer-lasting batteries 

Understanding how lithium incorporates in amorphous silicon nitride, and how the structure of the material changes in the initial charging stage, could be key to making batteries that last longer. To explore what drives this structural change at the atomic level, Emilia Olsson’s Materials Theory and Modeling group at ARCNL joined forces with Jörg Meyer’s group at Leiden University, whose research focuses on energy conversion dynamics at material interfaces.  

Using computer models, the researchers saw that during the first charging cycle, some silicon and nitrogen atoms rewire their bonds as lithium enters the material. These atoms form a new, mixed network of lithium, silicon and nitrogen that stabilizes part of the structure. They discovered that the formation of this stable matrix of atoms is driven by the trapping of electrons to form polarons, or bound electron-atom pairs, which combine to form bi-polarons. 

Lead author Jonathon Cottom compares it to unfolding a camping chair: the first hinge allows movement, and the second latch locks the frame into a stable shape. Similarly, the first trapped electron triggers atomic rearrangements, while the second “locks in” the new configuration. These changes can impact the movement of lithium ions, but they also prevent the structure from collapsing under stress – a common problem in silicon-based battery materials. This novel insight into the atomic processes driving this material transformation is an exciting step towards designing longer-lasting rechargeable batteries. 

From problem to design principle 

Until now, charge trapping has been seen as a challenge that reduces battery efficiency. This research shows that it can actually be a design feature that helps stabilize these anode materials. “By understanding exactly how charge trapping becomes structure,” says group leader Emilia Olsson, “we can start to design materials that use this effect to their advantage.” 

In other words, if engineers can control where and how these charge-induced transformations occur, they could build batteries that balance capacity with long-term stability. The study reframes “charge trapping” not as a flaw, but as a tunable property that can make batteries more reliable. Their findings could help engineers design longer-lasting batteries for electric vehicles and renewable energy storage. 

A Hot Paper 

The paper, published as a Hot Paper in the Journal of Materials Chemistry A, highlights how atomic-scale modeling can guide the development of more sustainable and efficient energy technologies. The journal also selected the study for a cover image designed by co-author Lukas Hückmann, which can be seen on the first page of the article PDF. 

You can read the full open-access publication in the Journal of Materials Chemistry A. 

Reference 

Jonathon Cottom, Lukas Hückmann, Jörg Meyer and Emilia Olsson, Forged by charge: polaron-induced matrix formation in silicon nitride conversion-type anodes for lithium-ion batteries, Journal of Materials Chemistry A (2025) 13, 34260-34272.