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The market interest in high-capacity, safe, and low-cost energy storage has picked up as the increasing deployment of solar and wind generation produces surplus electricity that cannot be immediately consumed. Recently, researchers at Stanford University in the US state of California have successfully devised a rechargeable, water-based battery that has the potential to store vast amounts of electricity cheaply and safely. The Stanford research team is optimistic that this prototype manganese-hydrogen battery can evolve into an energy storage equipment that takes in electricity generated by renewable energies and feeds the power back to the grid when needed.
While solar and wind generation technologies have become popular, the intermittency of these renewable energies creates the problem of sudden power surpluses and shortages. Hence, the need for an efficient battery system to fill the gap between the sources of generation and the grid has become critical. Currently, the lithium-ion battery is the mainstream rechargeable battery technology on the market with the widest range of applications. However, building a high-capacity energy storage system using lithium-ion batteries (as some dubbed it “lithium-ion battery plants”) is considered a costly venture. Furthermore, lithium-ion batteries lose their charge over time, so they have to be replaced regularly.
The Stanford team’s manganese-hydrogen batty is regarded as a prospective grid-scale energy storage solution because it specifically addresses the issues of cost and lifespan. Yi Cui, who is a material scientist at the university and a member of the research team, explained that the manganese-hydrogen battery works by dissolving a special salt in water and inserting an electrode. The salt together with the water produces a reversible chemical reaction that stores electrons in the form of hydrogen gas.
This special industrial salt is actually manganese sulfate, which is commonly present in dry cell batteries, fertilizers, and paper products. Electrons in the solution will react with manganese sulfate, forming manganese dioxide at the electrode and hydrogen gas that picks up the excess electrons. The hydrogen can then be turn into electricity through other methods (e.g. burning or other chemical processes).
Since the generation of electricity from hydrogen gas is no longer an engineering hurdle, the main challenge for the research team is to show that their prototype water-based battery can be recharged. When testing the prototype, the researchers re-attached the power source to the depleted battery and found that the reaction can be reversed in a stable process. During recharge cycle, the manganese dioxide particles at the electrode combine with water to become the manganese sulfate. The restoration of the salt again creates excess electrons that are stored as hydrogen gas. This process is repeatable, thus allowing the battery to be recharged frequently.
The prototype battery, which represents the initial stage of the research, is about 7.6 centimeters tall and can generate 20 milliwatt-hours of electricity. This amount is just sufficient for an LED flashlight. Nevertheless, the Stanford team believes that their technology is scalable and can be applied to industrial grade energy storage equipment capable of achieving at least 10,000 times in charge/recharge cycles and having a lifespan of more than 10 years.
Based on the estimated lifespan of the prototype battery, Cui calculated that the cost of storing electricity needed to power a 100-watt lightbulb for 12 hours with the manganese-hydrogen battery would come to about USD 0.01. On the whole, the research data provided by the Stanford team show that this technology can meet the recommended standard set by the US Department of Energy for utility-scale energy storage systems (i.e. capable of storing/discharging at least 20 kilowatts in an hour, performing 5,000 recharges, reaching a lifespan of at least 10 years). Also, to make such a battery system practical in terms of cost, the entire system has to be at or less than USD 2,000, or USD 100 per kilowatt-hour for consumers of its power.
(The above article is an English translation of a Chinese article written by Daisy Chuang.)