Next-generation lithium batteries with metallic lithium anodes and solid ceramic electrolytes may be one step closer after a study found that dendrites grow from the lithium anode and disrupt the ceramic electrolyte in the process. two stages. The work gives researchers useful guidance on how to inhibit them and extend battery life.
Today’s commercial lithium batteries use an organic liquid electrolyte with a graphite anode. Lithium ions are reduced and intercalated into the graphite structure when the battery is charged, and oxidized and released on discharge. Charles Monroe, from the University of Oxford in the United Kingdom, describes the development of the alternating anode as one of the ‘transformative discoveries’ in the development of modern lithium batteries. “Lithium metal is extremely unstable – when you let it out of a liquid it looks like moss rather than flat metal, and it is also highly reactive, causing side effects,” he explains. and incapacitated. However, the alternating anode also has a much lower capacity than the pure lithium anode.
Replacing the liquid organic solvent with an ionic conductive ceramic solid could potentially solve both problems: the ceramic would maintain the shape of the interface with the metallic lithium electrode and would reduce side reactions. However, researchers have found that lithium tendrils called dendrites grow from the anode towards the cathode through dense ceramic electrolytes. They also form in liquid electrolytes because the cations are attracted to the nearest electron source. However, their appearance in a pottery is puzzling. Monroe described the texture of lithium as “more like cold butter than steel”. ‘The conventional wisdom is that soft materials won’t be able to penetrate hard materials,’ says Peter Bruce, a colleague of Monroe’s at Oxford: ‘That’s the question of the test: how is that possible? go out?’ Such dendrites can break the material, resulting in a short circuit.
Previous research has suggested that lithium deposition into microscopic cracks and holes in ceramics can lead to dendrites formation. In the new study, however, a team around Monroe and Bruce re-examined the process by incorporating the ubiquitous argyrodyte electrolyte lithium phosphorus sulfur chloride into a test battery and monitoring its formation and spread. crack transmission in real time using computerized x-ray tomography and computed tomography. other imaging techniques. Using this data and extensive modeling, the researchers showed that cracking occurs in two stages, with the cracks initially occurring at the voids. However, once cracks have formed, they will spread by being pulled out at the base instead of cutting at the top.
This may provide some useful hints for the development of more stable solid battery electrolytes: ‘The mechanical properties that define the start are local fracture strength at grain boundaries, whereas The mechanical property that determines propagation is fracture strength,’ explains Bruce. In particular, the researchers found that batteries operating under high pressure short-circuited five times earlier: ‘It is generally thought that applying stack pressure to the cell would be a good thing, and the only problem is you need more metal and more weight,’ he said; ‘What we’ve shown here is, even if you can live with that cost, you don’t want it.’
Materials scientist Kelsey Hatzell of Princeton University in the US says work ‘starts – pun intended – discards this’ [dendrite formation] that mechanism is barely understood.’ She says argyrodyte is just one type of ceramic electrolyte, albeit a very common one: ‘I would say the next two steps: the first is to find out if this is common to all substances. solid electrolysis or not – which I don’t think will happen. get it – and the second is to understand how this mechanism changes when you have a true alternating cathode.’