40-Year Enthusiasm for Energy Storage Batteries

The principle of a redox flow battery was first proposed in 1974 by NASA, USA. Almost at the same time, the National Institute of Advanced Industrial Science and Technology*¹ (AIST) launched basic research in Japan. Around 1980, the difference in demand for electricity between day and night started to emerge as an issue with the growing proliferation of air conditioners in Japan. A proposed measure was load leveling, storing oversupply power in the nighttime and using it in the daytime. A national project, the Moonlight Project, was started to develop four advanced energy storage batteries, including redox flow batteries. In this period, Sumitomo Electric was looking for new themes to overcome the tendency to rely on the power cable business. One of the new themes was an energy storage battery. In addition to power generation and transmission, energy storage was thought to be necessary in the future. Thus, a redox flow battery was chosen as a new development theme, which had development issues in materials. It was in 1982 that Toshio Shigematsu, a newcomer at that time, was assigned to develop the battery.

However, Shigematsu and other development members did not give up. They tried to use a vanadium electrolyte, which an Australian university proposed. When the developed battery was tested, it achieved high performance in an instant with the help of accumulated cell material techniques. The electromotive force was 1.4 times as large as that of the Fe-Cr electrolyte, the output was doubled, and the energy density was almost tripled. The generated hydrogen gas was extremely decreased. A gleam of light was seen on the way toward commercialization.

*1 Then the Electrotechnical Laboratory

The circumstances had changed in the latter half of the 1990s, when electricity deregulation had developed and the power rate decreased. Electric power companies changed their course of action. They were installing energy storage batteries at customer sites to sell inexpensive nighttime electricity in terms of effective use of nighttime power. In response to this need, Sumitomo Electric began to deliver redox flow batteries to universities and plants in 2001. However, Shigematsu’s and other members’ hopes were shattered. The redox flow batteries at that time had low durability and suffered from repeated troubles, such as the leakage of an electrolyte. It was difficult to solve these problems, and top management decided to withdraw from the redox flow battery business in 2005. After that, the members had to focus on troubleshooting.

The tide began to turn in 2009. The US proposed the Green New Deal initiative, and large-capacity storage batteries were required to store renewable energy. In Japan, a movement toward renewable energy was growing. While winding down the business, such as removing facilities, they were trying to find the causes of past problems and implement measures. Katsuya Yamanishi said that he felt the time was ripe.

In 2012, a 1,000-kW test system was constructed at the Yokohama Works, and verification tests of developed techniques were conducted. The facility was well received and encouraged dialogue with the markets. This verification led to a real-scale demonstration test at Hokkaido Electric Power Co., Inc (HEPCO) in 2015, funded by the Agency for Natural Resources and Energy, a demonstration project, the New Energy and Industrial Technology Development Organization (NEDO) project in California, USA, and adoption of redox flow battery systems by HEPCO Network.

Aggressive attempts to improve redox flow batteries are still being made at the same time. The most serious issue is a price that customers can accept. To reduce the costs, they are trying to increase output and energy density and are developing an inexpensive electrolyte.

The important factor in cost reduction is output power improvement. The key is cell stacks. The aforementioned Yamanishi and other members are making efforts to increase output power for performance improvement.

“We are improving materials for electrodes and membranes and developing a cell structure that can reduce pressure loss during electrolyte circulation to increase output power. Electrolyte development and higher output power are two sides of the same coin. We aim to develop materials for cell stacks and a structural design that are optimum for the characteristics of an electrolyte. In addition, it is necessary for cost reduction to downsize the container, considering the whole system in the big picture, such as an integrated storage system for components. We also aim to develop a system using a total optimization method,” said Yamanishi.

They are also concentrating on developing an inexpensive new electrolyte for next-generation systems. Tou Youyou has been developing a new electrolyte since joining the Company.