Are Lithium-ion Battery Safe?

- May 28, 2020-

Electrical outlets are safe, right? There are many in every home, and we don’t think twice about plugging stuff into and out of them on a regular basis. But if you stick a conductor into each pole, you will get electrocuted.  So don’t do that.

Similarly, one should avoid certain things when handling a Li-ion battery. For example, a Li-ion battery should not get hot, overcharged, overdischarged, or shorted.  Battery packs, and even individual cells, available on the market contain a Battery Management System (BMS) that prevents overcharge, overdischarge, or short-circuiting. So, the only remaining things to avoid are: physically abusing the battery and getting it hot. So don’t throw one off a bridge or into a fire.

The Boeing Scare
The Dreamliner is a marvel of engineering. Lightweight materials combined with battery power ensures the most cost-effective and fuel efficient airliner in existence. So what happened with the Li-ion battery that caused the fleet to be grounded and a ton of negative press? The battery in the Ethiopian Airline’s jet in London got caught in a fire that started somewhere else. In the Japan Airlines incident in Boston, the voltage dropped to zero indicating an external short. These are certainly not good things to have happen, but it should be noted that Boeing uses perhaps the most dangerous type of Li-ion battery – large prismatic Lithium Cobalt Oxide (LCO) cells. LCO is the most flammable cathode material that can be used. And large prismatic cells offer the worst heat transfer, making it difficult to dissipate heat formed inside the cell. The FAA-approved solution was simply to isolate the battery from external events by encasing it in a stainless steel box. Perhaps a safer chemistry or pack design is on the horizon for Boeing?

The Tesla Scare
The Tesla Model S is a beautiful machine. The battery pack is assembled out of roughly 7,000 cylindrical cells. The cathode material (Lithium Nickel Cobalt Aluminum Oxide, or NCA) is not the safest in terms of thermal runaway potential, but has a high energy density. However, each individual cell is small enough that it can dissipate heat efficiently. And if thermal runaway occurs in one cell, it can be constrained to that one cell. Moreover, there are numerous safeguards in place that monitor the status of each cell and avoid cell failure altogether. So why the bad press? Because, in several instances, drivers drove into a metal object that pierced the battery pack, shorting out the battery internally. These situation were easily detected, and the drivers instructed to pull over and get out of the car as the battery burned. Nobody was hurt. What would happen if an object, metal or otherwise, pierced a gas tank? Anyway you look at it the bad press is unfair, and the Tesla Model S remains one of the safest cars on the market.