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A containerized energy storage system (ESS) product showcased by SK on at InterBattery 2026, held at COEX in Gangnam District, Seoul, in March. / SK on

SK on announced on Oct. 28 that its energy storage system (ESS) had met the evaluation criteria for the large-scale fire test (LSFT) under UL 9540A, a North American fire safety testing standard.

UL 9540A is an ESS safety testing standard that evaluates the extent to which heat spreads to surrounding areas in the event of battery thermal runaway. The large-scale fire test simulates actual fire conditions to verify whether a fire spreads to adjacent containers, among other factors. The detailed evaluation requirements were strengthened in March this year.

The test results showed that heat from the container where the fire occurred did not trigger thermal runaway in battery cells inside adjacent containers. Temperatures inside the containers also met the evaluation criteria. SK on explained that its design, which distributes and releases heat over an extended period, suppressed sudden increases in the heat release rate and reduced the likelihood of fire spreading.

SK on plans to use the test report as a springboard to strengthen its presence in the global ESS market. In August, the company signed an agreement to supply lithium iron phosphate (LFP) batteries to U.S. ESS company NeoVolta Power. In September last year, it also signed a 1-gigawatt-hour (GWh) supply agreement with U.S. renewable energy company Flatiron Energy.

The company is also expanding its domestic business. In February this year, SK on secured 284 megawatts (MW) out of a total 565 MW offered in the second round of the central contract market. It is also converting 3 GWh of its Seosan plant's total 7 GWh production capacity in South Chungcheong Province into dedicated production lines for LFP batteries used in ESS.

"This test confirmed the fire safety of SK on's ESS, demonstrating its ability to suppress fire spread and maintain key safety performance even under actual fire conditions," an SK on official said. "We will continue to strengthen our safety technologies and product competitiveness, provide customized ESS solutions to customers and expand our presence in the global market."

                                                                                                           Kim Jeong-kyu