Forskningsprojekt Hi-C

Tailoring crystals for better performing batteries

Tuesday 28 Jan 14

Contact

Poul Norby
Professor
DTU Energy
+45 46 77 47 26

Projekt Hi-C’s primary goals

Project Hi-C's primary goals are to:

  • Understand the important interfaces in an operating battery on an atomic and molecular scale.
  • Characterize the formation and nature of interfaces in situ.
  • Devise methods to control and design interface formation, stability and properties.
  • Prepare artificial interface layers in order to study their mechanical and electrochemical properties.

This should result in better modifications or new surface coating of batteries to improve performance.

Eight European partners

The eight partners in Hi-C are the Technical University of Denmark and Haldor Topsøe A / S from Denmark, the Université François Rabelais de Tours and the Commissariat à l’énergie atomique et aux énergies alternatives (CEA) from France, Karlsruher Institut für Technologie and Varta Microbattery GMBH from Germany, the Swedish University of Uppsala and the British company Uniscan Instruments Ltd.

Efficient energy storage using batteries has increasing importance to the energy sector. A new European research project will aim to improve performance of batteries, especially lithium batteries.

The project "Novel in situ and in operando techniques for the characterization of interfaces in electrochemical storage systems", abbreviated Hi-C, has participants from eight European universities and companies from Sweden, UK, Denmark, Germany and France. The Danish participants are Haldor Topsøe A/S and DTU Energy Conversion.

The results of Hi-C will be important for large scale storage of wind energy where stability, storage capacity and especially the transport of ions and electrons in batteries is important.

A lot of energy to be stored

The perennial problem of wind turbines is that they only produce electricity when the wind blows, and when it happens they generate large amounts of power in a short time. Batteries used for storage of wind energy shall for this reason be able to store a lot of power and receive that power very fast.

"We are actually able to follow the crystal growth of interfaces in operando by using acoustic emission and sound waves and "see" what happens by listening and sending ultrasound."
Senior researcher Poul Norby, DTU Energy Conversion

"We need to improve the properties of this type of batteries, their durability and power densities, and how much and how quickly the power that can get into and out of a battery," says the project coordinator and senior researcher at DTU Energy Conversion, Poul Norby.

This can be done by changing the internal interfaces of the crystals in battery electrodes and using additives to create new custom made artificial boundary between electrolyte and electrode, hopefully leading to a positive effect on the ion transport properties and reactions in batteries.

The C of Hi-C relates to  how quickly power can be drawn out from a battery;  1 C equals a full discharge the battery in one hour. The Hi-C project will be an exciting challenge for DTU Energy Conversion which for many years has researched in batteries and interfaces using in-situ methods.

Live studies of working batteries

In Hi-C the researchers use in-situ-methods as well as in operando, which is looking directly into the battery while it runs, to study transport of ions live in the interfaces inside a battery.

Batteries contains many types of interfaces, e.g. between electrodes and electrolyte and within individual crystals, and even if the transport of ions in the material itself is very important, the ability to transport ions and electrons through the interfaces is often the limiting and hence the most important factor.

The problem with interfaces is that they are very, very thin and very, very difficult to measure.

"It is difficult to develop specific methods that can make you see both the surfaces of the individual crystals and at the same time keep track of the reactions inside interfaces," says senior scientist Poul Norby.

The partners in Hi-C have been carefully chosen to reflect the challenges, with each partner having unique expertise in different fields like electron microscopy, spectroscopy, surface analysis, electrochemistry and theoretical calculations and modeling. A key area is the X-ray diffraction and spectroscopy using extremely powerful X-ray sources, synchrotrons, which are found in Lund, Hamburg, Grenoble and near Oxford.

Seeing the crystals grow using sound

DTU Energy Conversion has a key role in the project due to the longstanding research of the department into lithium batteries. This includes calculations and modeling at the atomic level and in-situ studies. The challenge is to make an intelligent design of the interface, e.g. by using additives to change the interfaces and also tailor artificial layer of crystals rather than letting nature decide their growth.

"We are already in the process of developing micro-battery cells, where you can follow the electrochemical processes on the surface. This way we gain knowledge about their change and watch the interfaces at the same time. But we're working with very small elements. Crystals are less than a micrometer in size and the interfaces inside them 10-20 nanometers, so it is all very tiny and quite a challenge," says Poul Norby.

The measurements are done by putting sensors in commercial batteries and monitor what happens.

"We are actually able to follow the crystal growth of interfaces in operando by using acoustic emission and sound waves (done at CEA) and "see" what happens by listening and sending ultrasound," says the senior scientist.

New groundbreaking ways

The results of the acoustic emissions can be difficult to interpret, which is a problem in itself, but this is solved by combining the in operando experiments with data from experiments in situ and ex situ, where electron microscopy is used to watch the domains inside the crystals.

"By looking at the distribution of lithium and other chemical gradients, such as oxidation of each particle and the electrolyte, we‘ll get information that makes it possible to understand the data that we got through other experiments. And all the information is included in the electrochemical model of the battery."

Combining innovative interface studies with theoretical models haven’t been done before and the methods are so groundbreaking and generic, that they are expected to be extended to other materials.

"Hi-C will lead to suggestions for better modifications or new coating on the surface of batteries, which will improve the battery. Hi-C treads new paths and is expected to finish in spring 2017," says Poul Norby.

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