Dispute Erupts Over What Sparked an Explosive Li-ion Energy Storage Accident

Matthew N. Henry

A tiny following 8:00 p.m. on April 19, 2019, a captain with the Peoria, Arizona, fireplace department’s Hazmat device, opened the doorway of a container stuffed with extra than ten,000 energized lithium-ion battery cells, section of a utility-scale storage technique that had been deployed two years before by the nearby utility, Arizona Community Service.

Previously that night, at all-around 5:forty one p.m., dispatchers had gained a phone alerting them to smoke and a “bad smell” in the region all-around the McMicken Battery Electricity Storage System (BESS) web page in suburban Phoenix.

Sirens blaring, 3 fireplace engines arrived at the scene inside ten minutes. Shortly following their arrival, to start with responders realized that energized batteries were being associated and elevated the phone to a Hazmat response. Just after consulting with utility staff and selecting on a plan of motion, a fireplace captain and 3 firefighters approached the container doorway shortly right before 8:00 p.m., planning to open up it. The captain, recognized in a afterwards investigation as “Captain E193,” opened the doorway and stepped inside of. The other 3 stood close by.

The BESS was housed in a container organized to keep 36 vertical racks separated into two rows on either facet of a 3-ft-vast hallway. 20-7 racks held fourteen battery modules created by LG Chem, an eighty kW inverter created by Parker, an AES Advancion node controller made use of for details selection and interaction, and a Battery Security Unit (BPU) created by LG Chem.

The battery modules in flip contained 28 lithium-ion battery cells of Nickel Manganese Cobalt (NMC) chemistry. These modules were being connected in series, furnishing a for every-rack nominal voltage of 721 V. The total technique had a nameplate potential to source 2 MW of ability over one hour for a life time power score of 2 MWh. With 27 whole racks, there were being ten,584 cells in the container. Just after a whole working day of charging, the batteries were being all-around 90 % of potential.

With the doorway to the BESS container open up and Captain E193 at its threshold, combustible gases that had crafted up inside of considering that the incident commenced numerous hours right before gained a breath of oxygen and found an ignition source.

The gases erupted in what was described as a “deflagration event.” Firefighters just exterior of the incident scorching zone said they read a loud noise and observed a “jet of flame” increase some 75 ft out and twenty ft up from the doorway.

In the explosion, Captain E193 and firefighter E193 were being thrown against and underneath a chain-link fence encompassing the facility. The captain landed extra than 70 feet from the open up doorway the firefighter landed 30 ft away.

The captain’s injuries provided a traumatic brain harm, an eye harm, spine harm, damaged ribs, a damaged scapula, thermal and chemical burns, inside bleeding, two damaged ankles, and a damaged foot.

The firefighter endured a traumatic brain harm, a collapsed lung, damaged ribs, a damaged leg, a separated shoulder, laceration of the liver, thermal and chemical burns, a missing tooth, and facial lacerations.

The timeline and series of gatherings is not usually disputed. However, a dispute has erupted in new weeks over what particularly transpired inside of the BESS container at all-around four:54 p.m. that initiated a thermal runaway that cascaded across various battery cells.

In a report introduced in late July, the utility and its third-celebration investigator, DNV-GL, said that their evaluation of the evidence pointed to the failure of a single lithium-ion mobile as triggering the gatherings.

In a independent, preliminary report filed days afterwards with state officers, LG Chem, which equipped the li-ion batteries, challenged that acquiring. The South Korea-based mostly battery supplier said the APS report missed a quantity of specifics about the incident. These specifics, LG Chem advised regulators, indicated that the mobile thermal runaway commenced owing to “intense heating” brought about by a warmth source “such as exterior electrical arcing” on one of the battery racks.

Scott Bordenkircher, who served as APS’ Director of Technological know-how Innovation & Integration at the time of the incident, said in an interview that the utility accepts the conclusions of its third-celebration incident investigation, which was done by Davion Hill, Ph.D., the U.S. Electricity Storage Chief for DNV GL. “We have assurance in our third-celebration investigator,” Bordenkircher said.

In its 78-webpage report [PDF], DNV GL said that what was to start with believed to be a fireplace was in reality an comprehensive cascading thermal runaway event inside the BESS. That event was initiated by an inside mobile failure inside one battery mobile, recognized as mobile 7-2 on Rack 15. The failure was brought about by “abnormal lithium steel deposition and dendritic growth” inside the mobile, the report said.

The moment the failure occurred, thermal runaway cascaded from mobile 7-2 via each individual other mobile and module in Rack 15 via warmth transfer. The runaway was aided by the “absence of ample thermal barrier protections” amongst battery cells, which in any other case might have stopped or slowed the thermal runaway.

As the event progressed, a large total of flammable fuel was developed inside the BESS. Missing ventilation to the exterior, the gases established a flammable atmosphere inside the container. Around 3 hours following thermal runaway commenced, when firefighters opened the BESS doorway, flammable gases created make contact with with a warmth source or spark and exploded.

It was a “tragic incident,” Bordenkircher said.

It also was not the to start with time that a lithium-ion battery had failed.

The APS report detailed gatherings achieving back again to 2006 that associated thermal runaway gatherings in lithium-ion batteries. In one extensively report incident in January 2013, a Boeing 787-8 skilled smoke and warmth coming from its lithium-ion battery-based mostly auxiliary ability device. It was afterwards decided that the failure was brought about by an inside mobile defect, which was exacerbated as thermal runaway cascaded via all the cells in the battery pack, releasing flammable electrolyte and gases.

“The state of the marketplace is that inside problems in battery cells is a recognized concern,” said Hill. Even so, issues with the engineering have not been nicely communicated amongst, say, the own electronics sector and the automotive sector or the aerospace marketplace and the power marketplace.

“Overall, across the marketplace there was a hole in information,” Bordenkircher said. The engineering moved ahead so immediately, he said, that requirements and information sharing had not held up.

The McMicken BESS incident also was not the to start with for APS. In November 2012, a fireplace wrecked the Scale Electricity Storage Procedure (ESS) at an electrical substation in Flagstaff in northern Arizona. The ESS was created by Electrovaya and consisted of a container housing 16 cabinets made up of 24 lithium-ion cells.

An investigation into that incident decided that a severely discharged mobile degraded and affected a neighboring mobile, touching off a fireplace. The root induce of the 2012 incident was found to be defective logic made use of to management the technique.

The management logic had been up to date extra than two dozen instances for the duration of the 11 months that the BESS operated. But numerous missed opportunities could have prevented the fireplace that wrecked the device, the incident report said. It pointed in individual to an event the earlier May in which a mobile was “severely discharged” even as the logic was “continuously charging the mobile against the supposed layout.” Just after the May event, the logic was not changed to address that inappropriate behavior.

An APS spokesperson said that classes realized from this 2012 incident were being integrated into the layout and operation of the McMicken BESS.

In its 162-webpage rebuttal [PDF] of the McMicken incident LG Chem refuted the utility’s acquiring of fault with its battery.

The battery supplier said that based mostly on obtainable evidence, “metallic lithium plating did not induce an inside mobile failure main to the initial thermal runaway event” at the McMicken BESS facility. Rather, mobile thermal runaway commenced via intense heating of the affected cells brought about by an exterior warmth source, these types of as exterior electrical arcing on Rack 15.

LG Chem said that its very own third-celebration investigator, Exponent Inc., examined the inside mobile failure concept. It did so by forcing a parallel mobile configuration into thermal runaway. It then as opposed the ensuing voltage profile to the voltage profile recorded for the duration of the incident. It found that the two did not match, main to the conclusion that the explosion’s induce was not likely to have been “an inside limited inside a single mobile.”

The battery maker also said that details recorded for the duration of the incident confirmed a discharging present of four.9A (amps) present for the duration of the voltage excursion. It said that even though the APS report acknowledged that the present flipped from -27.9A charging to four.nine A discharging,“it supplied no explanation for the event.” To LG Chem, having said that, the reality that the discharging present was at four.9A, rather of zero, “means the present in fact flowed to someplace else,” supporting what it said was a possible double-point electrical isolation failure and not an inside mobile limited.

(Complicating the submit-incident investigation was the reality that the fireplace wrecked technique management electronics inside the container. That remaining dozens of battery modules energized with no way to discharge them. It took 7 weeks for the utility to figure out a plan to clear away the modules one by one and bleed off their saved power.)

The studies and their divergent conclusions signal the commence of competing interpretations of obtainable details as the utility and its battery supplier perform to come across a single induce for the incident.

“We really do not want a community argument about it,” said DNV GL’s Davion Hill. For him, the main point is that “we had a cascading thermal runaway that led to an explosive atmosphere” at the APS McMicken BESS. The objective now must be to make storage programs safer via requirements enhancement and data sharing.

Just after the incident, APS put a keep on BESS deployment across its provider territory. The engineering is found as crucial to conference the utility’s introduced targets to produce 100 % “clean energy” by 2050. Two other BESS programs that had been functioning at the time of the April 2019 incident were being taken offline they will stay idle right until retrofits can be developed and put in.

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