R+D CSIC

Latest trends in batteries

The International Battery Association meeting will take place in Barcelona next March, from the 10th to the 15th. It will congregate scientists working on batteries as well as companies and students from over the world.

The meeting, which is organized by the CSIC’s Instituto de Ciencia de Materiales de Barcelona (ICMAB) (and that has already closed the registration due to the limited meeting room capacity) will serve as a specialised forum to show and discuss the latest research on this area.

M Rosa Palacin, a scientist at the CSIC’s Instituto de Ciencia de Materiales de Barcelona (ICMAB) and head of the meeting organizing committee, explains some of the latest research strategies. Most of them focus on the search of new materials to make batteries safer, cheaper and more efficient, and also to extend its life, in order to satisfy the growing demands from portable electronics and automobile industry.

Improving materials

Batteries are chemical devices for storing energy. They are composed of two parts, the electrodes, made of electrochemically active compounds and separated by another material, the electrolyte, which is electronically insulating but does conduct ions. The battery supplies energy through the electrons movement, going from one electrode to the other through an external circuit. This electron movement is compensated by an ionic transference troughout the electrolyte.

When the active material of one of the electrodes is exhausted the battery is fully discharged. If the process can be reversed applying an external electric current, batteries can be recharged. The number of times a battery can be recharged keeping a certain capacity (approximately 80% of the initial capacity) is known as the battery cycle life (or battery lifespan). To enhance power, duration or security, is necessary to improve the electrode and electrolyte materials.

Energy and power

Lithium based tehnology has allowed a high development of portable applications thanks to its great energy and power density. There is not a single lithium-ion technology, as the electrode materials can be diverse. The choice of the most suitable materials depends on the priorities. For exemple, the lithium iron phosphate batteries are less toxic and safer than lithium cobalt oxide but they have less energy. M.Rosa Palacin explains: “In some cases power is the priority, in other cases it is energy. Electric tools like drills for instance, are used briefly but they need a high density of energy, power. On the contrary, applications such as mobile phones need more energy than power”.

To enhance power, duration or security, is necessary to improve the electrode and electrolyte materials.

Other materials nowadays under research are metallic alloys, mostly based on tin and silicon, which could highly improve the capacity if they could be applied to the negative electrode. Also the so called “conversion materials” (such as the iron or cobalt simple oxides) are being studied. They can offer high capacity but still have unsolved problems like the big difference between the charge and discharge voltage.

Safer batteries

A common problem is safety. The electrolyte is an organic and inflammable solvent. Sometimes, extreme conditions (overload or short-circuit for instance) can provoke this material to burn.  This is what apparently happened in the recent case of a Boeing 757 Dreamliner and in the case of an electric car which after an accident set on fire.

The research looks for new materials to prevent these situations. For instance, new electrodes that don’t release oxygen (suchas lithium iron phosphate) or electrolytes that have components (ionic liquids) or additives to reduce inflammability.

More futuristic are the lithium-sulphur and the lithium-air batteries, which have arisen many expectations. They have essential problems to solve yet. M. Rosa Palacin explains that “they could give a very high energy density at a lower price, but they have to overcome many obstacles”. The most viable seems to be the lithium-sulphur battery but not in the short-term: “The sulphur dissolves within the electrolyte, therefore ruining the battery in a too brief period of time”.

Refering to nanotechnology, Palacin points out that it can be helpful only sometimes, when the used materials are very safe. Otherwise it’s not a good option because nanomaterials often have less density and can exacerbate adverse secondary reactions, such as the descomposition of the electrolyte.    

Sodium batteries

A promising line are the ion-sodium batteries. The team led by M.Rosa Palacin, at the Instituto de Ciencia de Materiales de Barcelona, is working on them. “Sodium is cheaper than lithium, which is a rare and scarce element, and their chemistry is similar”, explains Palacín.

“Some people propose using lithium always. But we think that in cases where the weight is not so important, like in stationary applications, sodium is a better option as it is abundant and unexpensive”. The maximum capacity attainable for sodium-ion batteries remains to be ascertained but scientists think it could be similar to that of lithium-ion if suitable materials are unraveled.

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