The future belongs to lithium ion batteries?

Experts opine that the future belongs to electric vehicles, but  challenges persist. One  challenge is the power supply. Batteries have to be safe, reliable and reasonably priced.

The most promising are lithium ion cells, which offer the highest energy density. These batteries are used in electric cars, for the storage of wind and solar energy, for medical examinations or to propel deep-sea vehicles. 

Quick charging and discharging: Renewable energy sources (wind or solar power) often deliver more power than needed. So, how to store surplus energy? While lithium-ion batteries can store lots of energy, they take a long time to charge.

Super-capacitors, however, can quickly store energy, but their energy density is low.

Researchers at the Fraunhofer Institute for Silicate Research Centre for Applied Electrochemistry in Würzburg, Germany, are working on a battery that combines the benefits of lithium-ion batteries and super-capacitors.

Depending on the requirements, they intend to produce energy storage media that they can set either to the high energy density of a battery or to the high output density of a super-capacitor. For example: lithium-ion batteries that charge many times faster than conventional batteries.

Long service life through optimal cooling: Adding 10 degrees Celsius cuts the energy storage medium‘s life in half. An ingenious cooling system is a must. For electric car applications, researchers have developed a well-cooled battery system, which  consists of 12 flat lithium cells with a fluid-fed cooling plate on each side.

For peak performance from the cooling plates, they have simulated their form and tailored it to the geometry of the individual battery cells (using computer modelling).

The effect is: the cooling plates spread heat uniformly in the battery while reducing the temperature rise to a few degrees, even under large load. They use a circuit board to each battery to create a module-management system which  monitors the temperature, charge and deterioration of the individual cells in the battery module.

It transmits the data to the battery system‘s central control unit. Special algorithms based on stochastic particle filters were developed.

Air cooling helps. They stack the individual lithium cells, separated by narrow strips of special polymer foam, with a fan to circulate air. Strips offer two benefits: One, they create channels in the interstices for air to flow and dissipate the heat. Also, with the cells lying directly atop the foam strips, the design is very stable.

Cooling is optimal. The cells are no warmer than the air drawn away from them. Cooling elements are less than 20 per cent of the cells' total  weight.   

Improved safety for lithium cells: Safety is an important factor. With lithium batteries, the aim is to prevent short-circuiting. Short circuits occur if the two electrodes come in contact with one another.

Separator layers are designed to keep them apart. Another safety benefit is: the ceramic structures are flame-proof, making it more difficult to ignite the electrolytes. This is important for lithium batteries with very high energy densities.

(Max Babi is a metallurgist and tech enthusiast. The views expressed by the author are his own and not of CIOL)

Earlier post by the author: 3-D printing of unmanned aerial vehicle that flies