Two fires in two months at a California utility-scale battery storage facility highlight the long-known fire risk of lithium-ion batteries.

“Although the flames were extinguished in a few days, the metaphorical smoke is still clearing,” an MIT Technology Review story on the fire said. The Moss Landing Power Plant, where the fires occurred, is the world’s largest collection of batteries on the grid, the article says.

Lithium-ion batteries have been in widespread use since the 1990s, but their fire risks remain a concern for states and localities. Earlier this month, Yorktown, New York, passed an ordinance outlawing the use of lithium-ion battery and other Tier 2 battery energy storage systems — those that produce between 600 kWh and 10 MW of energy. 

Better batteries

Given their role in storing energy from solar and other renewable sources, lithium-ion batteries are on track to become more, not less, common in on-site backup systems, the American Clean Power Association says. And despite those high-profile incidents, the batteries are safe and getting safer, the advocacy group says. 

“Energy storage battery fires are decreasing as a percentage of deployments,” the group says in a fact sheet. “Between 2017 and 2022, U.S. energy storage deployments increased by more than 18 times, from 645 MWh to 12,191 MWh, while worldwide safety events over the same period increased by a much smaller number, from two to 12. During this time, codes and standards regulating energy storage systems have rapidly evolved to better address safety concerns.”

Lithium-iron phosphate, or LFP,  batteries are actually safer than previous designs, such as the nickel-manganese-cobalt batteries that are used in electric vehicles, the group says. 

“LFP cell failure results in less energy release and a lower probability of fire,” it says. 

In addition, energy storage systems today incorporate features to avoid propagation of cell failure within the battery, contributing to safety. “Lessons learned from earlier ESS incidents have been reflected in the evolution of codes and standards,” ACP says.

Risk management

Facilities with battery energy storage systems on site can take steps to minimize the risk, according to a UL Solutions safety primer. 

The first is to understand why fires occur. Lithium-ion batteries are sensitive to heat and contain a flammable electrolyte solution. If the batteries get too hot or the electrolyte solution leaks onto something hot, the battery can catch on fire. Once that happens, the fire can burn hot enough to melt metal, making it susceptible to spreading to other batteries in the system. “Fires can … cause a building to collapse,” the primer says. 

A thermal runaway incident is another potential source of battery fires. This is when a cell within a battery malfunctions and starts a cycle of self-heating. If the cell heats up enough, it can lead to a fire and what’s known as cell-venting – the release of gases from inside the battery. 

“Violent cell venting is characteristic of thermal runaway incidents,” the primer says. “The intense heat can lead nearby cells into thermal runaway.”

Following safety protocols can minimize the risk of overeating and thermal runaway incidents, the safety primer states. Keep the batteries in a well-ventilated, cool space; be careful not to let batteries get damaged; and, if there is a damaged battery, don’t use it. 

“External damage includes deformed, dented, or broken parts, melted plastic, signs of corrosion and frayed wires,” the primer says. “Internal damages are indicated by hissing, crackling, or popping sounds; rattling loose or dropped parts; visibly swollen cells; heat; smoke; or an odor of battery electrolyte. Batteries that will not accept a charge or provide power indicate possible internal damage.”

Damage can lead to battery fires in a number of ways, many of them having to do with short-circuiting. Among other things, there’s a thin film inside the battery separating the cathode from the anode. If the integrity of the film is compromised because of battery damage, that can cause an internal short circuit.

Short-circuiting can also be caused by abnormal temperatures or air pressure and progressive internal damage due to improper charging and discharging, among other things, according to the safety primer.

“Heat produced by short-circuit incidents can cause thermal runaway,” UL Solutions says.