On May 12, the 2025 (11th) China Overseas Returnees Entrepreneurship Competition, hosted by the Overseas Returnees Entrepreneurship Park Working Committee of the China Association of Technology Entrepreneurs, was successfully held at the Changsha Overseas Returnees Entrepreneurship Park. After fierce competition through offline roadshows, on-site defense, and evaluation, ZH Energy successfully made it to the semi-finals with its “High Safety and Low-Cost Sulfur Iron Flow Battery Long-Duration Energy Storage Technology” project.

With the continuous expansion of the global wind and solar power generation installed capacity, the intermittent power supply characteristics have created an urgent demand for long-duration energy storage systems. The self-developed high-performance, low-cost sulfur iron flow battery technology by Zhonghe Energy has the following core advantages:

- High safety with no risk of combustion or explosion: The use of aqueous electrolytes, which are non-flammable, eliminates the risk of high-temperature expansion and deformation.
- Wide availability of raw materials and controllable costs: The sulfur iron flow battery uses sulfides and complex iron compounds to prepare the electrolyte. The raw materials are large-scale industrial chemicals with low prices.
- Full liquid electrolyte with no phase transition risk: There is no physical change of ion insertion and extraction, no generation of solid metal or gaseous phase transitions, and the inorganic compound structure is stable and non-degradable.
- High-temperature analysis shows stable substructure without the need for cooling equipment: The system does not produce precipitation at high temperatures, and the reaction activity is even better. Therefore, there is no need for a high-temperature cooling system, which can save system costs and operating energy consumption.
- Low marginal cost of electrolyte with significant long-duration system advantages: The cost advantage is more evident in longer discharge duration systems and is suitable for 6-12 hour daily energy storage applications.

In the energy storage field, cost is the core factor determining the feasibility and promotion value of a technology. Based on the cost analysis by ZH Energy’s NeLCOS® cost calculator, the levelized cost of energy storage shows that as the operating duration (especially over 6 hours) increases, the unit energy storage cost of each technology drops significantly. This reflects that the battery cost is spread over more cycles. The sulfur iron flow battery has the optimal full-cycle unit cost and remains stable at 12 hours of long-duration operation, demonstrating excellent stability and long-term economic viability, highlighting its economic benefits for long-term applications.

ZH Energy as the world’s first company to commercialize sulfur iron batteries, relies on the nearly 20 years of experience of its chief scientist, Dr. Xie Wei, in the field of American flow batteries. In collaboration with Professor Liu Suqin’s team from Central South University, they have developed an innovative sulfur iron electrolyte system. This has led the way in bringing sulfur iron flow battery technology from laboratory research to market commercialization, filling the industrialization gap in the sulfur iron technology route of flow batteries. In April, at the 13th International Energy Storage Summit in Beijing, ZH Energy launched the world’s first 125KW/1MWh sulfur iron flow battery system and will carry out demonstration projects this year. It is worth noting that the sulfur iron battery technology verification system jointly implemented by the company with State Grid and Central South University has been stably operating for several months, with all performance indicators meeting the design requirements.

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