However, there have always been concerns over their fire safety – as after several charge and discharge cycles, potentially dangerous tiny lithium fibres, known as dendrites, can form on the carbon anodes.
These fibres can short circuit the battery, causing it to overheat and catch fire. This can also happen if the battery is charged too quickly, where Li is deposited on the carbon-forming dendrites rather than inserting into the carbon.

To resolve some of these safety issues, a new study has developed an easy and accurate method to examine the inside of the batteries, using nuclear magnetic resonance (NMR) spectroscopy to examine how batteries behave under different conditions.

Published in Nature Materials [Bhattacharyya et al., Nature Materials (2010) doi: 10.1038/nmat2764], the research represents a new method for seeing, and quantifying the extent of, Li metal dendrite formation in functioning lithium-ion batteries before the signatures of these dendrites are seen electrochemically. The method should identify under what conditions they form, and to assess different strategies to prevent them forming.

The research team, from Stony Brook University in New York, the Commonwealth Scientific and Industrial Research Organization in Victoria, Australia, and the University of Cambridge in the UK, is using NMR spectroscopy to see within a minute, 1cm long, battery enclosed in an aluminium bag. This is the first time that scientists have been able to measure the amount of dendrites formed, as they cannot be quantified using a scanning electron microscope.

Team member, Clare Grey, pointed out that “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.”

The team now hope to screen different electrolytes for dendritic growth in Li anode-containing cells, to develop a better understanding of why these dendrites form, and under what charging regimes, and also to look at bigger batteries, in order to determine where in the cell the Li dendrites form. Future research will explore different electrode morphologies, and may even use MRI methods to examine the Li metal deposition.