Battery Design Challenges

One of the biggest challenges our modern AC electric power grid faces is the fact that energy must be produced in real-time as it is demanded. There simply does not exist a large-scale method of storing electric power at the power company's convenience. Certain techniques, such as pumping water uphill during off-peak hours to be released to spin turbines during peak hours, can help but are inefficient and impractical.

The holy grail of power storage has always been rechargeable batteries with massive storage capacity. Most of the research into batteries has concentrated on making durable, safe, high-density batteries for portable devices. Lithium-ion batteries power our MP3 players, cell phones, and laptop computers for hours on end in a convenient, lightweight package, but are extremely expensive and not scalable to the large, high-output needs of industrial, commercial, and residential power generation. What the power companies need is a scalable battery that can survive tens of thousands of charge-discharge cycles over a decades-long useful life, with a power output measured in Megawatts.

New MIT TR10 Liquid Battery Prototype

Donald R. Sadoway, professor of materials chemistry at MIT, has lead a design team to develop a novel prototype battery to meet these needs. Professor Sadoway's revolutionary approach was the opposite of traditional battery design: rather than take a material that could hold a charge and work on increasing its current output, he took a material with a high current output and worked on making it capable of holding a charge.

What his design team produced was a prototype battery completely unlike traditional designs in that it has no solid cathode or anode. Instead, the TR10 uses three liquids that naturally flow into layers because they have different densities. Molten magnesium (the cathode) floats on top of a layer of sodium sulfite (the electrolyte) which floats on a layer of molten antimony (the anode). As the battery discharges, magnesium and antimony ions dissolve into the electrolyte, and as it charges, the ions return to their original layers. This gives the battery an unusual property, the three layers change relative volumes as the battery charges and discharges. These materials were only used for the prototype, the team has not divulged the materials used in later designs.

The advantages to this battery design are enormous. Most attractively, the battery can cost as little as one-third the price of traditional battery designs. The liquid design is extremely robust, there are no solid parts to crack or degrade over time. The current output is tens of times higher than traditional solid battery designs as well because the ions don't have to move through a solid medium, they can travel freely through the molten metals. Finally, the design is easily scalable, you could make one the size of a soda can or the size of a swimming pool.

However, the design is not practical for portable electronics, or even electric vehicles. The three liquids that amke up the battery float on top of each other due to their different densities. This means that the battery must be stationary, sudden movement will cause the layers to mix together until they naturally separate again. While this doesn't damage the battery, it does render it useless except in stationary applications. But it is ideal for these stationary applications, being cheap and easily scalable.

Oh yeah, and the molten metals need to be kept at about 700°C (1300°F). So there's that too.

What the team doesn't know yet is what the failure modes are for this design. Traditional batteries have limited charge/discharge cycles because the solid components can crack and degrade over time and use. These are not concerns with the TR10 liquid battery, but surely the system has its limitations. The research now is focused on what these limitations are and what the useful lifespan of the battery might be. Professor Sadoway believes the design could be ready to market in as little as five years.

Potential Uses

In a video interview with Professor Sadoway, he covers the major drawbacks of green energy production such as solar and wind power. These are unpredictable, unreliable sources of energy, so in order to be useful for helping with peak power demand they would be best utilized generating power whenever they are available and storing it until that power is needed. This new battery would be ideal for this purpose, being scalable to large capacities and having extremely high power output that could meet the demands of the power grid. For reference, New York City has a peak power demand of 13,000 Megawatts and would require a TR10 battery covering 60,000 square meters (about 15 acres) to meet this demand, although it is unlikely anyone would want to run an entire city off of one.

Similarly, a residential house with a battery the size of a 30-gallon garbage can (the sort placed on the curb on garbage day) could run with battery assistance during peak load times (for example when air conditioners are turned on in the early afternoon) to reduce the strain on the power grid. It could then recharge during off-peak times when the grid has spare capacity, for example in the early morning when the sun is up but demand is low so spare solar energy is abundant, or at night when traditional coal and nuclear power plants have spare capacity and rates are cheap.

This is one of the most exciting developments in battery technology in a long time. This revolutionary design has enormous potential to level out the power demand on the electric grid and improve our utilization of green, non-polluting energy sources. Likewise, it could make the idea of a whole-house UPS back-up a reality, brief outages and voltage sags in the power distribution grid could go entirely unnoticed by the residential consumer. While we won't be seeing liquid batteries in our cell phones or cars, homes and businesses everywhere could see huge benefits in reliability, cost-savings, and carbon footprints.

Technology Review article published by MIT (with picture of the layered design)
Video interview with Professor Sadoway

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