Synchrotron light for industrial battery research

While the electronic devices we use every day are growing ever more advanced, they're still limited by power. The battery hasn't advanced in decades and both big technology companies and automotive companies that are making electric vehicles, are all too aware of the limitations of the battery systems available to them. While chips and operating systems are becoming more efficient at saving power, we're still only looking at a day or two of use on a smartphone before having to recharge.

Technology companies and car manufacturers are pumping money into battery development but energy storage is a complex area to follow. Batteries have multiple uses and multiple technologies, with some being quite different - such as flow batteries vs lithium ion. Other technologies are characterised by more minor distinctions such as the different types of lithium ion batteries which possess different chemistries pertinent to the role they are to carry out (electric cars vs. stationary storage, for example).

In most areas of the energy market the solution is fairly simple, you construct the resource, connect it to the grid and harvest energy from your source; wind or solar for example. Batteries, by contrast, are much more complex. You can absorb or release energy over specific timeframes in varying quantities and their use can vary from market to market, region to region, and country to country, An excellent example of this complexity is displayed within the automotive industry where electric vehicles for consumer use require high capacity batteries to lengthen the travel range between recharging stops. On the other hand, electric buses that make regular stops at points equipped with charging outlets require faster charging electrical energy storage. In this situation, supercapacitors, which can handle the high frequency nature of charging and discharging, are better suited.

Specific markets also call for a different order of priorities. The Electric and Hybrid Vehicles consumer markets generally call for higher capacity and the lowest cost possible to the consumer, whilst large scale grid storage seeks lower cost, but not necessary high energy density.

Here at Diamond, using our B18 Core EXAFS beamline, scientists from France, in collaboration with researchers from the UK, have investigated the structure and performance of the triplite form of Li(Fe1-βMnβ)SO4F as a potential Li-ion battery material. Intensive studies have shown that this phase exhibits the highest Fe3+/Fe2+ redox voltage of any inorganic compound to-date, but the complex interplay between structure, properties and function still required further investigation. Many available techniques employ ex situ approaches and the challenge here was to examine these battery materials under their true operating conditions - in situ.

X-ray Absorption Spectroscopy (XAS) is an ideal technique for in situ local structure and oxidation state studies on Fe-based materials, as it enables researchers to probe the changes that occur in materials during electrochemical cycling without being affected the electrolyte, carbon, or binder that are used to construct functioning cells. In this study, the in situ measurements performed on an operating battery cell revealed that the iron undergoes an oxidation state change from Fe3+/Fe2+ during Li de-insertion, while there were no notable changes in the Mn K-edge.

These results reveal the iron to be the electrochemical workhorse of this system, with the manganese complicit in the structural transformation to the triplite phase. It is these kinds of local structure analyses afford researchers insight into the reactions occurring in battery materials, allowing them to probe in greater detail the structure-property-function relationship in these important materials. You can read the full case study here....

An alternative to Li-ion batteries that is emerging is Lithium-sulfur batteries (Li-S) which have the potential to be drastically cheaper than conventional Li-ion batteries due to the low cost of sulfur. Lithium-sulfur (Li-S) batteries have been pursued as an alternative to lithium-ion (Li-ion) batteries for powering electric vehicles due to their ability to hold up to four times as much energy per unit mass as Li-ion and are 3 to 5 times lighter than a conventional lithium-ion battery. However, Li-S batteries don’t come without some problems. For instance, the sulfur in the electrode can become depleted after just a few charge-discharge cycles, or polysulfides can pass through the cathode and foul the electrolyte. Another issue Li-S batteries face is the difficulty of ensuring that they operate safely at high temperatures due to their low boiling and flash temperatures.

Nevertheless, Li-S batteries are one of the most promising technologies for the future and it is this potential that has prompted researchers from Germany and Amsterdam to perform sulfur K-edge X-ray absorption spectroscopy (XAS) measurements on Li-S batteries on the I18 beamline here at Diamond Light Source. Spatially resolved XAS with a small X-ray beam in the specially designed cell, allows experimentation at different positions in the battery cell, enabling researchers to unravel electrode- vs. electrolyte-only processes.

Using this technique, the researchers were able to obtain information about intermediates present in the cathode and the separator of an operating Li-S battery during discharging and charging. These identified pathways are expected to assist in reaching higher storage capacities in Li-S batteries and avoid deactivation by guiding both the development of models of Li-S battery operation and the design of improved cathode structures and electrolyte components.

This is just a brief insight into the type of battery research that is carried out here at Diamond. Recent studies also include research into conventional intercalation cathodes for lithium batteries, fundamental research focused into better understanding the structural and electronic processes occurring on electrochemical cycling, and optimisation studies of the composite design of battery cathodes in Lithium-rich, Mn-based composites, one of the most promising candidates for electric vehicle applications (EV/HEV/PHEV).

If you would be interested in reading more, check out the links below...

Leading the World in exploiting high speed light for super slow science

Imaging of lithium deposits gives clue to battery life

Three-dimensional micron-scale imaging of electrodeposited lithium microstructures

New electrode insights for sodium-ion batteries