We Need to Get Better at Building Electric Car Batteries
By: Sam Abuelsamid
Tags: Battery, Electric Vehicles, Technology, Engineering, Cars

We Need to Get Better at Building Electric Car Batteries

BMW i3 electric car. Photo: Jens Schlueter/Stringer/Getty Images

If we’ve learned anything from Tesla over the past decade, it’s that no matter how innovative and disruptive your product might be, manufacturing safe hardware is hard. Building anything in high volume is a challenge that’s significantly amplified by the complexity of vehicles. Traditional processes like welding, painting, and assembly are hard enough, but the difficulty level multiplies when you look at products like battery cells.

In recent months, three automakers have had to stop sales of electrified vehicles as a result of batteries experiencing thermal runaways, which is a fancy engineering term for catching fire. BMW and Ford have both told dealers to stop selling a number of plug-in hybrid vehicles following fire incidents while Hyundai is doing the same for the Kona electric. As a result of fires with the Ford Kuga plug-in hybrid, Ford has delayed the production launch of the North American equivalent, the Escape PHEV.

Approximately 170,000 vehicle fires happen annually in the United States out of a total vehicle population of 290 million. Out of that total vehicle fleet, approximately 4 million feature high-voltage battery systems including hybrids, plug-in hybrids, battery electric, and fuel cell electric models. Figures aren’t available for how many electrified vehicles experience fires, but a Ford spokesperson said that out of more than 900,000 hybrid vehicles sold over the past 15 years, none are known to have experienced battery fires.

While battery fires aren’t particularly common, they are problematic when they happen. At its basic level, a cell consists of positive and negative electrodes which sandwich a separator, and the whole assembly is surrounded by an electrolyte material. Thermal runaways are generally triggered when there is a short circuit between the electrodes. This most often happens when a cell is physically damaged such as in a crash or if there is a manufacturing defect.

When an internal combustion vehicle ignites for whatever reason, but most likely a fuel or oil leak onto a hot surface, extinguishing it is fairly straightforward. As we learned in science class, fire requires an ignition source, fuel, and oxygen. Starve the fire of either the fuel or oxygen and it goes out. When gasoline burns, you can smother it with water or foam and it goes out and generally stays out.

There’s no indication that batteries are any more prone to fires than gasoline vehicles, but the aftermath can be harder to deal with.

Batteries are a different story. The electrolyte that acts as a catalyst for conductivity in the cell consists of an organic compound mixture that contains oxygen. When a cell overheats, the electrolyte gives off oxygen. If the heat level reaches the ignition point, that oxygen will actually feed the fire internally, even if you smother it. In the famous crash of Apple engineer Walter Huang in his Tesla in 2018, the resulting battery fire took many hours to extinguish.

It’s also not uncommon for burning batteries to reignite hours or days after being extinguished due to damage to adjacent cells. This happened in 2011 after the first fire in a Chevrolet Volt. A poorly installed home charger caused the original fire. But two days after the vehicle carcass was hauled off to a wrecking yard, the battery reignited. There’s no indication that batteries are any more prone to fires than gasoline vehicles, but the aftermath can be harder to deal with.

These fires were all triggered by external sources, either crash damage or charging issues. But sometimes the fire is caused by a manufacturing issue. This was the case with the recent Ford and BMW problems.

Sources familiar with the situation at both Ford and BMW have confirmed that the fires that began while the plug-in hybrids were charging have traced the root cause back to a manufacturing issue with the cells. Both automakers use cells produced at the same supplier plant. Aluminum and copper particles from the welding process for the cell containers have been contaminating the interior of the cell, which in turn is leading to short circuits while charging the batteries.

This is by no means the first time that cell manufacturing flaws have resulted in fires, and many cell manufacturers have experienced problems. Back in 2011, the original Fisker Karma experienced issues with cells catching fire and in 2013, the Boeing 787 was temporarily grounded following battery fires on two aircraft. In the 1990s, multiple manufacturers of laptop computers had recalls in the wake of battery fires.

If you ever visit a cell manufacturing facility, you’ll find the environment is more like an infectious disease laboratory than a traditional car parts plant. The areas of the factory where electrodes are processed, rolled, or folded and packaged are all pristine. The cell assembly area is in a positive pressure room where the inside air pressure is kept above the ambient pressure outside to prevent contamination.

Anyone that enters this area has to wear a “bunny suit” that covers their entire body including the head and face. Most of the processing is completely automated to limit any interaction with the equipment or the cells.

If you ever visit a cell manufacturing facility, you’ll find the environment is more like an infectious disease laboratory than a traditional car parts plant.

The cell supplier for the affected Ford and BMW vehicles is making process changes to prevent this sort of contamination from happening again. Still, in manufacturing, there are rarely any guarantees that nothing has gone wrong. That’s why there are quality assurance departments, to make sure that the processes are right to begin with, that they are properly followed, and that any discrepancies are caught early.

Ford isn’t taking any chances, though. It has developed its own battery stress test. Once the cells are assembled into a battery pack for the plug-in Kuga and Escape, it will go through a new testing regimen before the pack is installed in a vehicle. European and North American plants are both implementing this testing procedure where they assemble the battery packs. BMW will likely do something similar with its battery packs.

Ultimately, while any verification method is important, it is a band-aid. Optimizing quality requires getting back to the root of the problem whether that is a product design issue or a manufacturing process flaw. Quality has to be baked in from the start, and as we grow the number of electric vehicles in the coming years, we’ll be building billions of cells and battery packs. Every step in the value chain has to work to minimize the number of dangerous and difficult to extinguish battery fires.