SK On is gaining momentum in its energy storage system (ESS) battery business, which has emerged as an alternative amid the electric vehicle "chasm" — a temporary slowdown in demand. The company is nearing new ESS supply contracts exceeding 10GWh with U.S. energy developers and other clients. This represents half of SK On's annual order target and is seen as encouraging evidence that the company's safety-enhancing technologies are resonating in the North American market.
According to battery industry sources on January 13, SK On is in discussions with multiple customers including Flatiron regarding ESS battery supply contracts. The battery supply volume exceeds 10GWh, estimated at 1 trillion to 1.2 trillion won ($700 million to $840 million) in revenue. The company expects to finalize contracts as early as the second quarter.
SK On previously signed its first lithium iron phosphate (LFP) ESS battery supply contract with Flatiron in September last year for 1GWh, while securing preferential negotiation rights for a 6.2GWh energy development project. Flatiron, headquartered in Colorado, specializes in designing, constructing, and operating large-scale battery energy storage systems.
If SK On secures all the projects currently under discussion, it would fulfill half of its 20GWh global ESS battery order target for this year. Less than a year after agreeing to supply 1GWh of LFP batteries to Flatiron, SK On's order backlog in the North American market would surge to over 10GWh.
Industry observers attribute the interest from North American clients to the safety-enhancing technologies SK On has extensively applied to its ESS batteries. Fire incidents in ESS batteries can lead to uncontrollable damage including power outages, making product safety the industry's top priority.
SK On's flagship safety technology is Electrochemical Impedance Spectroscopy (EIS), a core component of its fire prediction system. EIS analyzes internal impedance components — including electrolyte resistance, interface resistance, and diffusion resistance — based on frequency-specific voltage responses measured by injecting micro-currents into the battery. This enables early detection of abnormal signs such as cell aging and internal short circuits, offering higher precision than conventional voltage and temperature-based battery management systems (BMS).
SK On has also implemented dual valve and liquid immersion technologies to extinguish fires after they occur. The dual valve structure uses both active and passive valves to detect changes from fire incidents and introduce coolant. The active valve opens when sensors detect temperature and voltage exceeding threshold levels. The passive valve is designed so that when ambient temperature rises above the threshold, internal components burst to open the valve. When both valves open, coolant is introduced.
The liquid immersion technology submerges the entire pack in coolant released through the dual valve system to rapidly stabilize temperatures. The system is designed to prevent thermal runaway in the early stages of a fire and minimize damage spread.
Building on these safety technologies, SK On is targeting over 20GWh in global ESS battery orders this year. The company is accelerating the conversion of EV production lines at its Seosan Plant 2 in South Chungcheong Province to ESS production to expand capacity. The Seosan Plant 2 is expected to house dedicated ESS lines with capacity up to 6GWh.
In the United States, SK On has begun converting some EV battery production lines at its Georgia facility to ESS production. The company aims to begin mass production of LFP ESS batteries in the second half of this year.
"In the past, price and supply capacity were the main competitive factors for ESS batteries, but recently fire safety and operational stability have become the key criteria determining orders," an industry official said. "Companies that prove their safety technology competitiveness will succeed in differentiating themselves in the North American ESS market."
