Scientists have identified a reason why lithium batteries in laptops and mobile phones may overheat and catch fire.
Cambridge University researchers said the growth of metal fibres, called dendrites, could cause short circuits.
Nuclear Magnetic Resonance (NMR) spectroscopy, normally used to identify elements in molecules, has been adapted to "see" how the dendrites develop.
Researchers said it could help solve fire safety problems which have held up the development of lithium batteries.
Lithium battery technology is said to be crucial for progress on the next generation of electric cars.
When current batteries are charged quickly, minute lithium dendrites can form on carbon anodes.
These fibres can cause short circuits, causing the battery to rapidly overheat and catch fire, Professor Clare Grey, of Cambridge University's chemistry department said.
"These dead lithium fibres have been a significant impediment to the commercialisation of new generations of higher capacity batteries," she said.
"Fire safety 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 transport applications.
"Now that we can monitor dendrite formation inside 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."