Getting down to details: Magnetometry insights into fast-charging batteries

Conversion-type metal selenides are materials that have shown promise for next-generation energy storage. Specifically, they offer higher storage capacity than other anode materials, charge faster, and maintain stable performance at a large temperature range of −20 C to 50 C.

Zhu et al. created a model of one type of metal selenide — cobalt selenide encapsulated in nitrogen-doped carbon (CoSe@N-C) — to determine the underlying mechanism that makes these materials so powerful.

“Our primary motivation was to uncover the microscopic origin of the ultrafast interfacial kinetics observed in conversion-type metal selenides, which has remained largely unclear,” said author Qiang Li.

The researchers chose CoSe@N-C for their model due to its well-defined spatial confinement and tunable porosity, amount of CoSe, and interface quality. Batteries with CoSe@N-C anodes undergo a conversion reaction when combined with a storage mechanism: During discharge, CoSe reacts with lithium or sodium ions to form a tight interface between an electric conductor and an ionic conductor.

This interface can store extra charge, and by using operando magnetometry — a technique to study changes in a magnetic field while a battery is in use — the researchers could observe this electron-scale process in action.

Based on this investigation into the CoSe@N-C model, the researchers found they could quantify space-charge storage and learned more about how the spatial alignment of the interfaces can improve storage capacity.

“Future conversion-type materials must be designed with a strong emphasis on spatial confinement to maximize the contribution of the space-charge storage mechanism,” Li said. “By developing a well-defined spatially confined CoSe@N-C model platform, we sought to provide direct experimental evidence for space-charge storage, elucidate its role in delivering extra capacity and fast kinetics, and ultimately establish a physical design principle for next-generation ultrafast, wide-temperature energy storage materials.”

Source: “Quantifying space-charge storage in spatially confined selenides: Operando magnetometry insights for fast-charging and wide-temperature Li/Na-ion batteries,” by Ding-Ding Zhu, Zhong-Han Song, Shu-Cheng Xu, Ri-Zhen Sun, Hong-Yuan Song, Qing-hao Li, Yan He, Gui-Huan Chen, and Qiang Li, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0332753 .