Magnetometry to measure the state of lithium-ion batteries

Scientists at Germany’s Johannes Gutenberg University Mainz (JGU) and Helmholtz-Institute Mainz (HIM) have presented a non-contact method for detecting the state of charge and any defects in lithium-ion batteries, using atomic magnetometers to measure the magnetic field around battery cells. Their work has been published in Proceedings of the National Academy of Sciences.

The demand for high-capacity rechargeable batteries is growing, and so is the need for a form of sensitive, accurate diagnostic technology for determining the state of a battery cell — particularly given reports of serious injuries resulting from the explosion of e-cigarettes and the restrictions on taking certain types of mobile phones on aeroplanes. The success of many new developments will depend on whether batteries can be produced that can deliver sufficient capacity and a long, effective life span.

“Undertaking the quality assurance of rechargeable batteries is a significant challenge,” said Dr Arne Wickenbrock, a member of Professor Dmitry Budker’s work group at JGU and HIM. “Non-contact methods can potentially provide fresh stimulus for improvement in batteries.”

Prof Budker’s group has now achieved a breakthrough by using atomic magnetometers to take measurements — an idea that came about during a teleconference between Prof Budker and his colleague Professor Alexej Jerschow of New York University. They developed a concept and, with close cooperation between the two groups, carried out the related experiments in Mainz.

“Our technique works in essentially the same way as magnetic resonance imaging, but it is much simpler because we use atomic magnetometers,” said Dr Wickenbrock, referring to optically pumped magnetometers that use atoms in gaseous form as probes for a magnetic field. Prof Budker’s group uses atomic magnetometers for fundamental research in physics, such as in the search for dark matter and in attempts to solve the riddle as to why matter and antimatter did not immediately annihilate each other after the Big Bang.

In the case of battery measurements, the batteries are placed in a background magnetic field. The batteries alter this background magnetic field and the change is measured using atomic magnetometers.

“The change gives us information about the state of charge of the battery, about how much charge is left in the battery, and about possible damage,” said Dr Wickenbrock. “The process is fast and, in our opinion, can be easily integrated into production processes.”

Image caption: Yinan Hu, a member of Professor Dmitry Budker’s research group at JGU, holding a battery cell alongside a device which measures the state of charge. Image ©Arne Wickenbrock.

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