Rechargeable lithium-ion batteries don’t last forever. Over time, it retains less charge and eventually turns into a brick from the power source. One reason is hidden, leaky hydrogen, a new study suggests.
unwanted hydrogen protons It fills the molecular slots at the positive end of the battery. There is less space for charged lithium atoms, or ions, which help maintain reactivity and conduct charge, scientists reported on September 12. science.
New research has identified a series of undesirable chemical reactions that unfold when battery electrolytes, which are supposed to transport lithium ions, inadvertently release hydrogen into the anode or cathode. This “causes all kinds of problems” and reduces the capacity and lifespan of the battery, says Gang Wan, a materials physicist and chemist at Stanford University. “Batteries lose energy even when they are not in use.”
Past explanations of energy loss in batteries have focused on the movement of lithium ions. Some researchers have hypothesized: Hydrogen atoms may also play a roleBut hydrogen has been difficult to observe because it is so small and ubiquitous. So Wan and his colleagues replaced the hydrogen in the electrolyte of the cell-sized battery with deuterium, a heavier variant of hydrogen. The researchers then used high-performance X-ray imaging and mass spectrometry to track the movement of the deuterium. Using their results and theoretical calculations, the team showed that hydrogen plays a “dominant” role in cathode charge loss.
The study improves our knowledge of the opaque chemistry unfolding inside batteries, which makes it “really important,” said Bart Bartlett, a materials and inorganic chemist at the University of Michigan in Ann Arbor, who was not involved in the study. This hints at possible routes to improve battery life, such as adjusting battery chemistry to avoid hydrogen reactions.
The study also highlights an unrecognized problem in the ongoing push for batteries that require increasingly higher voltages as engineers aim to store more energy in smaller cells. Higher voltage cathodes are more reactive and more likely to attract hydrogen, so the higher the battery voltage, the more of this “protonation” or “hydrogenation” will occur. “The trade-off is that we don’t think we’ve properly evaluated what we’ve done or understood why,” says Bartlett.
But the scientists evaluated only one type of battery and scenario, he said. More research is needed to understand how broadly the findings apply.
Jacqueline Edge, a battery researcher and engineer at Imperial College London, says that if the team’s observations prove replicable, they will likely lead to better, longer-lasting batteries that will accelerate innovations such as long-range electric vehicles. At the same time, improvements in battery life will minimize the need to mine minerals that go into battery cells, such as cobalt or lithium. This has negative environmental and social consequences.SN: 5/7/19). It could be a double sustainability win, she says.
