SK On Demonstrates ESS Fire Safety in Large-Scale Fire Test

• SK On’s ESS meets UL criteria for large-scale fire testing
• No thermal runaway observed in adjacent container during testing
• SK On to accelerate global ESS market expansion following successful test

SEOUL, October 28, 2026 – SK On, a leading global battery manufacturer, announced that its energy storage system (ESS) met UL 9540A evaluation criteria in a large-scale fire test.

UL 9540A is a widely recognized North American test standard for evaluating fire and heat propagation during battery thermal runaway events. 

The large-scale fire test (LSFT) simulates real-world ESS fire scenarios to assess the risk of fire spreading to adjacent containers. In March 2026, the testing requirements were strengthened to introduce more clearly defined criteria for evaluating fire propagation.

During the test, no thermal runaway was observed in the battery cells of the adjacent container. Temperature measurements inside the container also met the applicable evaluation criteria. 

SK On attributed the results to its ESS design, which allows heat to dissipate gradually over an extended period. This helps prevent sharp increases in heat release rates and reduces the risk of fire spreading to neighboring containers.

SK On plans to accelerate its expansion in the global ESS market following the successful test.

In August, the company signed an agreement to supply lithium iron phosphate (LFP) batteries to U.S.-based ESS provider NeoVolta Power. In September 2025, SK On also signed a 1-gigawatt-hour (GWh) ESS supply agreement with U.S. renewable energy company Flatiron.

SK On is also expanding its presence in the South Korean ESS market. In February, the company secured 284 megawatts (MW) of ESS capacity, accounting for more than half of the 565 MW awarded in South Korea’s second round of competitive bidding for ESS projects.

The company is currently converting 3 GWh of its existing 7 GWh production capacity at its Seosan plant in South Korea into dedicated LFP battery production lines for ESS applications.

"This test confirmed the fire safety of SK On’s ESS, demonstrating its ability to limit fire propagation and maintain key safety performance under simulated fire conditions," an SK On spokesperson said. "We will continue to enhance our safety technologies and product competitiveness to provide customized ESS solutions and expand our presence in the global market."
 

About SK On
SK On is a global leading battery & trading company committed to technological innovation for a better, sustainable future. SK On was launched as an independent company in October 2021 after SK Innovation, South Korea’s largest energy company, decided to split off its battery business unit. SK On merged with SK Trading International in November 2024 followed by SK Enterm in February 2025 in a strategy to secure sustainable growth.

SK On aims to accelerate the green energy transition by leveraging its global production base and R&D capabilities, as well as its manufacturing and quality management know-how. 

Headquartered in Seoul, South Korea, SK On has a worldwide presence with battery plants currently operating or in construction across the United States, Europe, and Asia.

For more information, visit: http://eng.sk-on.com/