Li-ion batteries are used in many electronics, ranging from hearing aids to pacemakers and digital cameras. Despite their various applications, they also have their fair share of flaws.
Notably, lithium batteries have been in the spotlight for a number of negative reasons. Frequent incidents have been reported involving lithium batteries exploding and those issues contributed to significant safety concerns regarding their use. To get to the bottom of them, Michigan Technology Institute researchers examined the underlying architecture of Li-ion(Lithium-ion) batteries. A thin layer of polypropylene prevents the battery from short-circuit which means if this layer gets bypassed, things get pretty heated, pretty quickly.
These batteries contain a flammable electrolyte. In addition to this, it contains LiPF6 (lithium hexafluorophosphate) that can burn your skin. Despite such a risky, volatile architecture, these are widely used in the industry. The reason being that lithium batteries have a high energy-to-volume ratio.
Researchers examined nanoscale defects in lithium metal to better understand how lithium dendrites affect battery function. Image Credit: Sarah Atkinson/Michigan State.
Whenever a safety incident occurs, our first intuition is to look for flaws at the production level, which was precisely the reason behind the Samsung Note 7 incident, where poor design and strict hardware demands (slim smartphones), caused the battery electrodes to bend, eventually creating a short-circuit. The industrial market and competition for the battery to be low cost and feature extended battery time while requiring minimal charging resulted in insufficient manufacturing—which ultimately caused battery failure.
A very similar statement was made by Erik Herbert, assistant professor of materials science and engineering at Michigan Tech. He stated “The very thin solid-state electrolytes and high current densities required to provide the battery power and short charging times expected by consumers are conditions that favour lithium dendrite failure, so the dendrite problem must be solved for the technology to progress.”
A graph depicting the defect danger zone, the zone most likely to cause device failure by enabling the formation and growth of lithium dendrites. Image Credit: Tess Peterson/Michigan Tech.
A Unique Approach to Studying Failure
MTU researchers approached the Li-ion battery failure problem from what could be described as a unique approach. They adopted a “smaller the better” concept and observed that lithium’s stress-relieving mechanism is inefficient at micro-scale than its macro-scale mechanism.
At a smaller scale, the stress relief mechanism is changed from dislocation to diffusion. At a microscopic level, when the stress relief method uses diffusion, lithium can support 100 times the stress it could support on a macroscopic scale. Failure occurs in what researchers at MTU call, the danger zone. This is when a surface defect (pore size, roughness) of an SSE (Solid State Electrolyte) is too big for diffusion but small for dislocation. In those situations, high stress in the batteries can cause a catastrophic failure of SSE, which in return causes the battery failure.
This research will help further identify the defects in lithium batteries, as researchers will now carry research on the mechanical behaviour of lithium at a smaller scale. This will contribute valuable insight into some real-world conditions, ultimately helping them come up with solutions to prevent such failures.