A series of reports concerning battery swelling in Apple’s new iPhone 8 have thrown battery inspection into the tech and manufacturing spotlight once again. Lithium ion batteries continue to remind us of the trade offs with high density power sources. Why does swelling occur in lithium ion batteries? Swelling mostly occurs when gasses from one or more cells escape. A little-known fact to the general public is that batteries are pressurized and any additional pressure can cause damage to the components integrity. What can nondestructive x-ray inspection tell us about the issue? The chemical reaction that causes these gasses to escape can come about through overheating, overcharging or faulty controller components. In this post we explore these usual suspects using our TruView X-ray inspection platform.
Pictured below are a couple x-ray images of the most common cell arrangement in smartphone batteries. These stacks are disrupted when excessive oxidation of the battery chemicals (electrolytes) occurs. Individual cells or the entire battery itself can expand. Depending on how rapidly the gasses expand the cells could overcome the battery casing and explode, leading to fire hazards. In Apple’s case, no breaches have been reported, although the batteries have swelled enough to destroy the phone.
The underlying cause is overheating, but the overheating can occur via natural temperature increases as well as faulty charging controllers. The x-ray images below depicts a typical control board for a lithium ion battery. The voiding seen on some components can be acceptable to a certain degree, but excessive voiding can cause issues. The ribbon connecting the main board to the rest of the circuit can also presents issues when it has been damaged or tampered with. Failures in these areas can cause rapid chemical changes outside of specified limits. These violent changes in chemistry keep engineers at major manufacturers up at night; they also remind the manufacturing industry of the benefits of having non-destructive x-ray inspection systems available.