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Hybrid Cathode Boosts Energy Density of Lithium-Sulfur Batteries

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MIT researchers developed a technology that can give a major boost to lithium-sulfur batteries.

Energy storage technology is still struggling to keep up with the advances in electronics, renewable energy generation, electric vehicles, and all gadgets that require wireless power or delay in power usage. Lithium-ion batteries are still the leaders in the industry, although they do have their own limitations, especially when it comes to weight.

Lithium-sulfur batteries triggered quite a lot of interest, mainly because they give a promise for a lighter technology. The innovation here, however, has been quite slow. Scientists have tried a lot of tricks and ideas, but nothing has managed to bring the performance of these batteries to the desired level. The main hurdle to overcome comes from the cathode. It limits the technology to only two possible choices, and each was associated with a compromise. The choices are between having a light and big battery, or a small and heavy battery.

Now a team of innovators from MIT, the Samsung Advanced Institute of Technology, Tongji University, the Chinese Academy of Sciences and the Songshan Lake Materials Laboratory recently came up with a new development. They designed a hybrid cathode for both lithium-sulfur and lithium-ion batteries that promises better energy density.

The aim of the team was to come as close as possible to the most desired technology- small, light, with great energy density.

They came up with a solid cathode, which comprises of compressed particles made of pure sulfur and Chevrel-phase molybdenum sulfide. These particles increase the electrical conductivity of the cathode, which in turn reduces the need of carbon. In fact, when compared to typical sulfur cathodes, the new invention needs only 10%.

When the team tested the technology they were quite impressed by its performance. In their article published in Nature Energy, they reported some pretty impressive numbers.

The three-layer battery, which they built, has capacity of 1000 mAh. It is still a prototype and under development, but even before optimization, the battery could outperform some of the existing technology.

To give you a sense of the numbers. A typical lithium-ion battery has energy density of 265 watt-hours per kg, and 700 watt-hours per liter. Lithium-sulfur batteries can get to 400 watt hours per kg and per liter.

When the new hybrid cathode is used in a lithium-sulfur battery, it can reach 360 watt-hours per kg, and 581 watt-hours per liter. This means that in terms of gravimetric density, it is better than lithium-ion batteries, while in terms of volumetric density, it is better than lithium-sulfur batteries.

Unfortunately, there is still one major limitation that prevents this cathode from becoming the next best technology. Its lifespan is very limited. However, the team is determined to solve this issue as soon as possible, by focusing this time on the anode. All their efforts are now put there.

We will follow the developments and keep you posted.

Image (c) MIT

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