Kategori: Energy & Batteries

Image Credit: Yutaka Tsutano, US. CC by 2.0.

To most people mobile devices like smartphones are so much more than simple everyday objects. In personal messages, music, notes and calendars they basically contain our entire lives.

Despite the deep relationship to our smartphone, many do not hesitate to replace it with the newer model as soon as they get the chance. A report from 2016 suggests that in the UK smartphones are replaced by a newer version every two years.

Many people are not ware what the costs of this tech consumerism are. Smartphones, laptops and other consumer electronics contain up to 92 different elements and the origin of some is very problematic.

One example is the metal cobalt which is used in the lithium-ion batteries powering our devices. Cobalt normally comes from mines in African countries like the Democratic Republic of  Congo (DRC). Cobalt miners in these countries have to endure harsh working conditions with little to no safety regulations to protect them. The cobalt mines in DRC have also been linked to the use of child labour.

Other metals in mobile devices that have the same issues are gold, tantalum and tin. Gold and tantalum are used in the electric circuits while tin is contained in touch screens.

These metals, cobalt, gold, tantalum and tin, are also called ”conflict minerals”. The reason is that their trade has been linked to funding killings and violence in the DRC and other places.

In addition, the large scale mining and extraction of the metals needed to make a mobile device causes pollution and devours large amounts of energy, which in turn fuels global warming. And it does not stop there. After extraction the metals are mostly transported to China where the devices are assembled often by workers with low pay and poor working conditions.

So, what can we do as consumers to make sure our beloved smartphones do not have a negative impact?

1) Don’t upgrade your device unless you really have to. Even though it is tempting to replace your device as soon as the new version is released, it is best to use your old device until it really stops working.

2) Try to repair your device when it is broken. The two things that are most likely to break in your smartphone are the battery and the screen. Both can be replaced. Even though many current phone models cannot be taken apart and repaired easily, you can still try to repair the device yourself using YouTube tutorials. You can also send it to a shop for repair.

3) When you do have to part with your device, donate it to charity or sell it for example to a refurbishing shop. A lot of environmental problems are caused by mobile device disposal. Recycling is difficult because electronci devices contain so many different elements. Often they are sent to countries like Ghana, Nigeria or Vietnam for recycling. The easiest way to extract the valuable metals like copper, gold and aluminium is to take the devices apart and burn them. This process releases toxic chemicals into the air and the soil.

4) Consider buying a refurbished phone. From refurbishing companies you can get sturdy and cheap smart phones. None of the problems discussed above regarding mining and disposal are associated with them.

5) When buying a new device think carefully about what you want. Greenpeace’s ”Guide to Greener Electronics” is very useful if you want to buy a phone that has been produced sustainably. The guide rated the 17 world leading mobile device producers in the categories, Energy, Resource Consumption and Chemicals. The most sustainable device in their rating was the Fairphone made by a Dutch company with a grade B. It was followed by Apple in place two with a grade B-. A relatively young company producing more sustainable mobile devices is Shiftphone. This German start-up focusses on repairability and extending the lifespan os consumer electronics.

Image credit: Ben Mills.

 

The yellow powder in the image above is the element sulfur, which I am sure many people have seen before in school science lessons. Normally in chemistry classes, we are mainly taught about how bad the compounds made from this element smell. Examples are hydrogen sulfide with the distinct smell of rotten eggs and sulfur oxides. But could there be more to this powder? To find out, I have talked to Dr Matthew Lacey at Ångström Advanced Battery Center who is trying to build rechargeable batteries from sulfur.

Lacey is working on lithium-sulfur batteries (Li-S batteries) which consist of sulfur as the positive electrode (cathode) and lithium metal as the negative electrode (anode). When discharging (or using) these batteries, lithium and sulfur react to form the compound lithium sulfide and the process is reversed during charge. The advantage is the light weight of both sulfur and lithium, which leads to a very high energy density by weight. This gravimetric energy density of the batteries themselves could be up to two or three times higher than for conventional lithium-ion batteries according to Lacey. In addition, sulfur is abundant as well as a biproduct of the oil industry and, for these reasons, very cheap.

Nevertheless, Lacey admits that Li-S batteries also still have some drawbacks compared to conventional lithium-ion batteries. During discharge, sulfur dissolves in the electrolyte (the liquid placed between positive and negative electrode), where it can exist as a large number of different compounds called ”polysulfides”. These polysulfides can react with each other or be transported to the lithium foil (negative electrode) and react there. Especially, the reaction between polysulfides lithium results in very short lifespans for Li-S batteries. Strangely, the dissolution of sulfur in the electrolyte is an important part of how Li-S batteries work, but at the same time it is the source of severe problems. Another disadvantage is that, although the energy density per weight is high, the energy density per volume of Li-S batteries is rather low since lithium and sulfur are light, but have low densities.

Lacey is mainly working on a part of the battery called the ”binder”. In order to build a Li-S battery, sulfur and conductive carbon powder have to be attached to a conductive substrate, the current collector. Binders are the glue that stick sulfur and carbon powder to the current collector surface. Together these components form the positive electrode. Lacey is trying to find new binders that can do more than just be the glue of the electrode. The battery scientist wants his binders to interact with the polysulfides in the electrolyte (described above) to extend the lifetime of Li-S batteries. Lacey and his co-workers have been quite successful in this quest during the past years and more about it can be read in this recently published article.

The battery scientist is also proud about a new method called ”intermittent current interruption” that he developed during the past years. This technique makes it possible to track the resistance in batteries over long periods of time and can be used for all kinds of batteries, not only Li-S batteries.

Despite the challenges, Airbus Defence and Space are developing Li-S batteries for the Zephyr “High-Altitude Pseudo Satellite”. Li-S batteries are the only rechargeable batteries with a high enough energy density per weight to run this ”pseudo satellite” when sunlight is not available in the shadow of Earth. In addition, the UK based company OXIS Energy is working towards the commercialization of Li-S batteries.

Nevertheless, Lacey believes that due the low cost of lithium-ion batteries, they will keep dominating most markets such as electric cars and portable electronics in the foreseeable future. But, he also says, that Li-S batteries are still interesting for applications where battery volume and cost are less important. Examples are defence or space where Li-S batteries could power soldier equipment or satellites. Hybrid electric trucks could be another future market for Li-S batteries with battery volume being less of a problem for trucks than for smaller cars.

 

 

 

Image credit: Ronnie Mogensen, 2017. The materials ”Prussian white” (left) and ”Prussian blue” (right) are studied for the use in new battery technologies. CC BY-SA IGO 3.0.

With the dawn of electric vehicles and plummeting costs for renewable energies, battery technology is playing an ever more important role in our lives. Today lithium-ion batteries (LIBs) are being used in electric vehicles and for stationary power storage of renewable energy, for example in the Tesla powerwall. They can also be found in portable electronics such as laptops and mobile phones.

The problem is that lithium is a rather rare element with an abundance of only 0.0017 % in the Earth crust, most of which is found in South America. This inherent shortage combined with the high demand have lead to an increase of the lithium price by 14 % in 2016 with the price surges most likely continuing in the future. It is even doubtful if Earth has enough lithium resources to support the transformation from the fossil fuel-based society we are today to one depending mainly on renewable energy.

I have talked to two scientists who are trying to tackle this problem, Assistant Professor Dr. Reza Younesi and PhD student Ronnie Mogensen from the Ångström Advanced Battery Center (Uppsala University, Sweden). They are working on new kinds of batteries called sodium-ion batteries (SIBs) and magnesium-ion batteries (MIBs). These batteries rely on the use of sodium or magnesium instead of lithium, but work based on the same ”rocking-chair-principle”. In these batteries, metal-ions travel between two different electrodes during charge and discharge. The main difference is the nature of the travelling metal-ions, i.e. sodium-ions are used in SIBs, magnesium-ions in MIBs and lithium-ions in LIBs.

The huge advantage of these new batteries is, according to Younesi, the high abundance of sodium (2.3 % in Earth crust, atomic number 11) and magnesium (2.9 % in Earth crust, atomic number 12) as compared to lithium (0.0017 % in Earth crust, atomic number 3). In addition, large amounts of sodium can be found dissolved in sea water. Their good abundance enables the production of cheaper batteries from sodium and magnesium.

Nevertheless, Younesi admits that these battery technologies also have some drawbacks. Both sodium and magnesium are for example heavier than lithium, which is indicated by their higher atomic numbers. This leads to an overall lower energy density of these materials in batteries. This means that sodium-ion and magnesium-ion batteries need to be much heavier than lithium-ion batteries in order to store the same amount of energy.

Another challenge is the search for new electrode materials as not all state-of-the-art-materials used in lithium-ion batteries work for sodium- or magnesium-based systems. In addition, electrodes in lithium-ion batteries usually contain other scarce, toxic and expensive elements like cobalt, nickel or manganese. But, Younesi says, in order to truly produce cheap batteries, even the electrodess have to be made from abundant and inexpensive raw materials. For this reason one focus of Younesis and Mogensens research are iron- and carbon-based electrodes for sodium-ion batteries.

The most promising material they are studying at the moment together with researcher Dr. William Brant is called ”Prussian white”. It is derived from ”Prussian blue”, a compound that you might remember from high school chemistry lessons for its bright blue colour. It can be seen to the right in the image above. Prussian blue is a salt containing potassium, iron, carbon and nitrogen. In Prussian white the potassium has been replaced with sodium making it suitable for the use in sodium-ion batteries. It also gives the material a more ”whitish” colour as seen to the left in the photograph above. According to Mogensen, the beauty of this compound is that it only consists of very abundant elements (i.e. sodium, iron, carbon and nitrogen) and that it is  non-toxic.

In the future, Younesi sees great potential for sodium- and magnesium-ion batteries to replace lithium-ion batteries in stationary applications such as the energy storage in solar and wind power plants or ”home wall” batteries. The reason for this is that the higher weight of sodium and magnesium is less important in these applications than in portable electronics or cars.

In fact, sodium-ion batteries have already been commercialized in other fields. The battery company Faradion based in Sheffield (UK) produces sodium-ion batteries, e.g. for electric bicycles. Other steps have been taken in France by the Centre Nationale de la Recherche Scientifique (CNRS) where a sodium-ion battery prototype has been built that can fit and run in a conventional laptop. Also, Younesi and Mogensen in Sweden are not missing out on this rapid development. They are working towards the commercialization of their Prussian white material in sodium-ion batteries. With such a high innovation speed, it seems only a matter of time until we will see a wide-spread utilization of these new battery technologies.

Image: Kári Sveinbjörnsson, 2017. Two perovskite solar cells from his research compared in size to a coin of one Swedish krona. CC BY-SA IGO 3.0.

In 2009 a Japanese researcher found out that a material called perovskite could convert sun light into electricity similar to silicon solar cells. Interestingly, this kind of material had already been known for quite some time. Perosvkite is the name of not only one particular material, but of different compositions sharing the same crystal structure, the perovskite structure. The first perovskites were discovered as early as 1839 in the Ural Mountains and were named after the Russian mineral expert Lev Perovski who first studied them. The new perovskite that has received a lot of attention for its possible use in solar cells is called methylammonium lead iodide, quite a tongue twister, which is why I will refer to it as perovskite.

I have talked to Kári Sveinbjörnsson, a PhD student in the Physical Chemistry Group at Uppsala University (Sweden), who is working on perovskite solar cells. He says that a great advantage of perovskite solar cells is the cheaper manufacturing processes. Producing silicon from sand (which consists of silicon dioxide) consumes large amounts of energy as temperatures over 2000 degrees Celsius are required. In addition, silicon in solar cells needs to be extremely pure which leads to a total of 14 manufacturing steps. Producing perovskite solar cells, on the other hand, requires lower number of  steps and much less energy. A solution of the perovskite is dropped on an electronically conductive glas substrate. It is then put into a rotating machine, called a spin coater, to evenly distribute the solution. This is carried out at 100 degrees Celsius to evaporate the liquid solvent.

One big drawback of perosvikite solar cells is their poor stability according to Sveinbjörnsson. Perovskite is especially sensitive to moisture in air. Therefore, it has a much shorter lifespan than silicon solar cells and can not yet compete with their lifetime of 20 to 30 years. However, a lot of research is being carried out to change that. Another disadvantage is the presence of the toxic metal lead in the structure (indicated by the full name methylammonium lead iodide). For this reason scientists are trying to substitute lead with tin or bismuth, two less harmful metals. However, this exchange comes at a cost as the substitution of lead decreases the efficiency of the solar cells.

The extremely fast development of their efficiency has resulted in great interest for perovskite solar cells. While only a few percent of sunlight energy were converted into electricity with the first perovskite cells in 2009, we are today at an efficiency of 22 %, not far from the 25 % of silicon cells. This is an incredibly rapid increase within only eight years. At the moment a lot of research is focussed on the upscaling of the production process. It can be seen in Sveinbjörnsons image above that perovskite cells for research are not much bigger than one Swedish krona coins. Therefore, upscaling is important to make perovskite cells large enough to cover big roof parts.

Perovskite solar cells need one transparent electric contact on the top, facing the sun, and one electric contact at the bottom (which does not have to be transparent) in order to create electricity. Normally, thin layers of gold or silver are used for this task, but they can easily disintegrate and start to move through the entire solar cell which lowers its efficiency and stability. The most important part of Sveinbjörnssons research has been carried out on this issue in a collaboration with Aalto University (Finland) and École Polytechnique Fédérale de Lausanne (EPFL, Switzerland). In this work so-called carbon nanotubes, in other words extremely thin threads made of carbon, were used as the bottom electronic contact instead of silver or gold which resulted in more stable cells. This approach could eventually lead to cheaper perovskite cells with longer lifespans.

To the question when we will be able to buy commercialized perovskite solar cells, Sveinbjörnsson answers that the falling prices of silicon solar cells make predictions difficult. But he believes that we could see the first large-scale perovskite modules with 15 to 20 % effeciency within the next five years. Some more research revealed that there are already a few companies working towards the commercialization of perovskite solar cells. One approach is for example to combine perovskite with silicon by putting a thin perovskite cell on top of a silicon cell. This way the total efficiency can be increased as silicon absorbs the red part of the sunlight and perovskite the blue-green part. It remains interesting to see when and in which form perovskite will be commercialized in solar cells in the next years.