Japan Develops Hydrogen Battery That Stores and Releases Hydrogen at 90 C

A cooler route to storing hydrogen

Researchers at the Institute of Science Tokyo have developed a hydrogen battery that stores and releases hydrogen at about 90 C, or 194 F, while reaching the full theoretical storage capacity of magnesium hydride. Conventional solid hydrogen storage systems using that material typically need temperatures of 300 to 400 C.

The team was led by Dr. Takashi Hirose, working with Assistant Professor Naoki Matsui and Institute Professor Ryoji Kanno at the Research Center for All Solid State Battery in Science Tokyo. Their findings were published in Science on September 18, 2025.

The prototype combines magnesium hydride with a new solid electrolyte, a material that lets electrically charged hydrogen move between the cell's electrodes. It reached about 2,030 milliamp hours per gram, equivalent to hydrogen making up 7.6 percent of the storage material's weight. The researchers report repeated storage and release at full capacity at the lower operating temperature.

Hydrogen can carry energy between places and hold it for later use without emitting carbon dioxide at the point of use. Storage remains a difficult part of that process. Compressed gas requires heavy, expensive tanks, while liquid hydrogen needs cooling to around minus 253 C.

A solid storage system operating near the boiling point of water offers different design choices for vehicles, industrial plants and equipment that stores renewable energy. The Japanese cell uses electricity to control the movement of hydrogen through a solid, reducing the need for the extreme heat used in conventional magnesium hydride storage. Turning the laboratory result into practical equipment will require larger cells, durable materials and tests of the complete system.

What is inside the cell?

Magnesium hydride, written as MgH2, is the storage material at the anode, one of the cell's two electrodes. Hydrogen gas serves at the cathode, the other electrode. A solid electrolyte separates them while allowing hydride ions to pass through. A hydride ion is a hydrogen atom carrying an extra electron, giving it a negative electrical charge.

The electrolyte has the chemical composition Ba0.5Ca0.35Na0.15H1.85. It contains barium, calcium, sodium and hydrogen, arranged in an anti alpha AgI type crystal structure. That framework is known for superionic behavior, meaning ions can move through the solid very quickly.

Barium, calcium and sodium occupy positions that create a network of sites and channels. Hydride ions hop between spaces described as tetrahedral and octahedral sites with little resistance. This movement gives the electrolyte high ionic conductivity even at room temperature.

The electrolyte also provides electrochemical stability. It separates the hydrogen electrode from the magnesium hydride while keeping the route for hydride ions open. Its solid construction avoids mixing problems and side reactions that can affect liquid systems, supports repeatable cycling and reduces safety risks associated with leakage or volatility.

The proportions of barium, calcium and sodium can be adjusted. Changing those ratios offers a research route toward better conductivity, stability and manufacturing methods. The present combination supplies the fast ion transport needed for the magnesium hydride cell to operate at about 90 C.

How hydrogen moves during charging and discharge

During charging, the anode releases hydride ions from MgH2. Those ions travel through the solid electrolyte toward the hydrogen electrode, where they are oxidized, meaning they give up electrons, and form hydrogen gas.

During discharge, hydrogen gas at the cathode is reduced, meaning it gains electrons, to become hydride ions. The ions move back through the electrolyte to the anode side. There, they react with magnesium to form MgH2 again, returning hydrogen to solid storage.

The process is reversible: the same material can store hydrogen and release it repeatedly at about 90 C. Applied voltage and current drive the movement of hydride ions during charging and discharge, putting hydrogen itself directly into the cell's electrochemical operation.

Electrical control replaces much of the intense heating required by thermal storage methods. That reduces energy losses and simplifies system design. The solid electrolyte handles rapid ion movement, while moderate heating helps the magnesium hydride reaction proceed at a useful rate.

Why existing storage methods demand so much

Compressed hydrogen tanks often operate at pressures of 350 to 700 bar. Compressing the gas consumes energy, lowering the efficiency of the complete process. The strong tanks needed to contain it also add weight and cost, particularly when the storage system must travel in a vehicle.

Liquid hydrogen provides dense storage but brings a different set of demands. Hydrogen must be cooled below 21 K, near minus 253 C, to liquefy. Maintaining those temperatures requires equipment that consumes considerable energy. Hydrogen lost through boil off is a continuing problem, especially in warm surroundings or when the stored fuel is used slowly.

Solid storage materials can hold hydrogen compactly at low pressure. Many widely studied hydrides, however, release their hydrogen only at very high temperatures. Supplying that heat complicates the equipment and reduces round trip efficiency, the share of energy recovered after storage compared with the energy put into the process.

Earlier electrochemical methods using liquid electrolytes have also faced difficulties. Hydride ions move poorly through liquids designed for lithium or sodium batteries, leaving achieved capacities far below the amount the storage solids can theoretically hold. The Japanese team's approach addresses that transport problem with a solid designed specifically for fast hydride ion movement.

Other solid storage materials, including complex hydrides such as alanates and borohydrides, often need catalysts and can still require high temperatures while reacting slowly. Magnesium hydride is light and abundant. Pairing it with a fast ion conductor changes which part of the process limits performance.

What the capacity and temperature figures mean

The prototype's capacity of about 2,030 milliamp hours per gram matches the theoretical capacity of magnesium hydride. The corresponding 7.6 percent hydrogen content by weight describes how much hydrogen the storage material can hold. Reaching that capacity at about 90 C combines substantial storage with a temperature that practical equipment can more readily manage.

The electrolyte conducts hydride ions rapidly even at room temperature, but the complete cell operates with moderate heating to keep the magnesium hydride reactions moving. The researchers report repeated storage and release at full capacity under these conditions, a combination earlier thermal and liquid electrolyte approaches had not achieved.

Operation below 100 C makes heaters, insulation, seals and safety measures simpler than in systems running at several hundred degrees Celsius. Less demanding heating also makes it easier to connect the storage cell to other equipment. Waste heat from a fuel cell stack or an engine could help maintain its operating temperature.

The result brings together high energy density, lower operating temperature and reversible cycling. Those features create a basis for integration into vehicles or stationary storage equipment, while practical development will depend on how the complete system performs beyond small laboratory cells.

Where the battery could be used

Hydrogen fuel cell vehicles need storage that is compact, safe, light and efficient. A solid storage module operating near the boiling point of water could reduce some of the burden associated with high pressure tanks. At a station, a module could absorb hydrogen produced on site and later release it on demand to supply a fuel cell stack.

Cars, trucks and buses could gain different packaging options if storage needs less equipment for very high pressures or extremely low temperatures. The reversible solid design offers a route toward lower costs and simpler storage arrangements, subject to the weight, size and performance of a finished module.

Solar and wind installations offer another possible use. When electricity is plentiful, an electrolyzer can use it to make hydrogen. The battery could absorb and hold that gas at low pressure, then release it to a fuel cell or turbine when demand rises or renewable generation falls.

Microgrids, islanded systems and remote facilities could use this arrangement where large tank farms are impractical. For these installations, the storage module would be one part of a larger energy system connecting hydrogen production, storage and electricity generation.

Steelmaking, ammonia production and refinery operations also need dependable hydrogen flows. A modular bank of solid storage cells could act as a buffer, absorbing brief changes in supply or output so that industrial processes continue steadily. Lower operating temperatures and solid construction could simplify placement inside plants and reduce permitting difficulties compared with cryogenic storage.

Heat, moisture and repeated cycling remain engineering tasks

A cell operating near 90 C still needs thermal management. Designers must provide heaters, insulation and controls to maintain temperature in cold weather and prevent overheating in hot conditions. Rapid changes in temperature during fast charging or discharge also need control to keep materials from cracking or degrading.

The electrolyte is a hydride containing several components and is sensitive to oxygen and moisture. Manufacturing it will require powders with the correct chemical proportions, particle sizes and purity. Producing dense separators without defects will require controlled environments and quality checks.

Magnesium hydride also reacts with water and oxygen, so a storage pack must keep air and moisture out. Hydrides expand and contract as they cycle, creating another durability challenge. Coatings, binders and control of pressure within the cell stack are development areas for maintaining good contact, low resistance and a long operating life.

The electrolyte's composition offers room for adjustment, but manufacturing must also deliver consistent results. A material that conducts ions well in a laboratory cell needs to retain that performance when produced and assembled in larger quantities.

A solid store still needs hydrogen safety equipment

Gas management remains part of the design because the cell stores and releases hydrogen. Equipment must prevent leaks and provide safe venting. Sensors, valves and regulators need to work with the solid storage stack so that the complete installation meets relevant codes and standards.

Compressed gas, liquid hydrogen and solid storage each place different demands on equipment. Compressed gas requires strong pressure vessels and energy for compression. Liquid hydrogen needs cryogenic machinery and measures to limit boil off. The new battery instead uses moderate heat and electricity to move hydride ions and hold hydrogen in a solid.

Avoiding cryogenic hardware and very high pressure vessels could simplify safety arrangements and reduce the energy consumed by supporting equipment. Vehicle developers will still have to assess the size, weight and cost of a complete storage package.

Stationary installations face a similar calculation across a larger chain of equipment. Electrolyzers, fuel cells and power electronics must be sized together with the storage system. Their combined round trip efficiency must compete with alternative ways of storing energy. Pilot projects at increasing scales will be needed to identify maintenance requirements and performance over extended operation.

What comes after the laboratory result?

Independent replication and larger cells are the next milestones. Larger cell formats and stacks need to demonstrate the same capacity and reversibility, along with stable operation across hundreds or thousands of cycles.

Developers will also need to measure how quickly the cells can charge and discharge, how they respond to repeated starts and stops, and how safely they behave under damaging conditions. These tests will help determine whether a storage system can meet the changing demands of vehicles, electricity networks and industrial users.

Automakers, energy developers and industrial gas suppliers will look at the cost per kilogram of stored hydrogen, energy efficiency across charging and discharge, and maintenance needs. Partnerships could support pilot installations combining electrolyzers, hydrogen battery modules and fuel cells if manufacturing methods become standardized and cycle life proves durable.

The development sequence begins with the published laboratory findings and moves toward tests of complete equipment:

• September 18, 2025: The team's findings were published in Science.
• September 20, 2025: The reported result combines operation at about 90 C with the full theoretical capacity of magnesium hydride.
• Next milestones: Independent replication, larger cells and stacks, extended cycling tests and pilot deployments. No dates were given for these steps.

The immediate advance is the combination of a fast hydride ion conductor and magnesium hydride storage at moderate temperature. Its practical value will depend on preserving that performance while adding the seals, heaters, gas controls and other equipment needed outside the laboratory.

Key Points

• Institute of Science Tokyo researchers report a hydrogen battery operating at about 90 C, or 194 F, compared with the 300 to 400 C typically needed by conventional magnesium hydride systems.
• Dr. Takashi Hirose led the work with Assistant Professor Naoki Matsui and Institute Professor Ryoji Kanno.
• The cell combines magnesium hydride, a hydrogen gas electrode and the solid electrolyte Ba0.5Ca0.35Na0.15H1.85.
• The electrolyte's anti alpha AgI type structure supports fast hydride ion movement even at room temperature.
• The prototype reached about 2,030 milliamp hours per gram, corresponding to 7.6 percent hydrogen by weight, with repeated storage and release at full capacity.
• Potential uses include fuel cell vehicles, renewable electricity storage and hydrogen buffers for industry.
• Development priorities include thermal control, protection from air and moisture, manufacturing consistency, cycle life and complete system efficiency.
• The findings appeared in Science on September 18, 2025. Larger demonstrations and independent replication are next steps.