NMR study aids battery safety

By helping them understand how these batteries behave under different conditions, the method could help researchers solve the fire-safety problems that have dogged the development of such batteries.

Lithium-ion batteries have enabled the development of many electronic devices, such as laptop computers and mobile phones. However, the batteries have one serious disadvantage: over several charge and discharge cycles, particularly if the batteries are charged quickly, minute fibres of lithium, known as dendrites, can form on the carbon anodes. These lithium fibres can cause short circuits, causing the battery to rapidly overheat and catch fire.

Prof Clare Grey of Cambridge University’s Department of Chemistry said: ’These dead lithium fibres have been a significant impediment to the commercialisation of new generations of higher-capacity batteries that use lithium metal as the anode instead of the carbons used today.’

Previously, scientists have used theoretical models and optical and scanning electron microscopes to study dendrite formation, but finding a way of quantifying the amount of dendrites formed has proved elusive.

Now, however, Prof Grey and her colleagues have demonstrated that they can use NMR spectroscopy to provide quantitative information about the nature of the metallic lithium deposited on lithium-metal electrodes.

The NMR methodology monitors structural changes that occur during the operation of the battery. The in-situ NMR studies allow the researchers to capture metastable phases, follow reactions between the electrolyte and the electrode materials and investigate the effect of rapid charging and cycling of the battery.

Prof Grey said: ’Fire safety is a major problem that must be solved before we can get to the next generation of lithium-ion batteries and before we can safely use these batteries in a wider range of transportation applications. Now that we can monitor dendrite formation inside intact batteries, we can identify when they are formed and under what conditions. Our new method should allow researchers to identify which conditions lead to dendrite formation and to rapidly screen potential fixes to prevent the problem.’

Last month Prof Grey was awarded the Royal Society of Chemistry’s John Jeyes Award in recognition of her world leadership role in using NMR methods to study structure and function in inorganic materials, particularly lithium-ion batteries.