Kategori: Energy & Batteries

Which batteries are powering spacecrafts?

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Image Credit: ESA–David Ducros, 2017, CC BY-SA IGO 3.0.

Batteries on the International Space Station (ISS)

In January 2017 two astronauts on the ISS went for spacewalks to upgrade power storage batteries outside the station. Nickel-hydrogen batteries originally designed specifically for space stations and satellites had been used during the first battery installation. They had reached the end of their lifespan and were replaced by more modern lithium-ion batteries which will be in service until the ISS is decommissioned 2024.

The advantage of nickel-hydrogen batteries was their long lifetime withstanding large numbers of charge-discharge cycles. But they were sensitive to ”battery memory” meaning they could loose part of their capacity if not charged and discharged completely during each cycle. The main task of the ISS batteries is to store the energy produced by the solar panels during its 45 minutes in sunlight. This electricity is used during the following 45 minutes in darkness wich the ISS passes through with every orbit.

Lithium-ion batteries have a much higher energy density than nickel-hydrogen batteries. Therefore, one lithium-ion battery can replace two nickel-hydrogen batteries, despite being smaller and lighter. In addition, lithium-ion batteries do not show a battery memory effect, but they are more sensitive to overcharging and need to be protected against it. They also typically have a lower lifespan than nickel-hydrogen batteries, but the lithium-ion batteries for the ISS have been specifically designed for 60000 charge-discharge cycles, i.e. a ten year lifespan.

Batteries on Satellites and Space Crafts

Just like the ISS, space crafts and satellites need access to energy when being in the shadow of a planet. Therefore, they normally also carry batteries for the storage of energy produced by sun light. Batteries are also needed to kick-start operating systems before the solar panels are unfolded. In addition, rockets rely on the use of high-power batteries for autonomous operation during the launch into space.

Some space crafts like ESA`s Huygens probe run with non-rechargreable batteries (lithium sulphur dioxide batteries) when solar panels are impractical. Space crafts venturing very far from the sun like the Cassini mission to Saturn or New Horizons to Pluto by NASA depend on electricity from so-called radioisotope thermoelectric generators (RTGs) instead of solar panels or batteries. These produce electricity from the decay of radioactive plutonium.

During the early days of space flight, nickel-cadmium batteries were used for energy storage. However, they were soon supplanted by the nickel-hydrogen technology described above. These are now in turn slowly replaced by lithium-ion batteries. Their biggest advantage for space travel is the high energy density meaning they can store a lot of energy at a low weight and small volume. One major challenge regarding the use of lithium-ion batteries in unmanned space flight is their sensitivity towards the extremely low temperatures in space. Another problem is the long battery lifespan of 1000 to 33000 cycles required in space missions which can take up to 15 years. Despite these obstacles work is ongoing to improve the lithium-ion battery technology for further applications in space.

A short history of batteries

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Image: Voltaic Pile by I, GuidoB, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2249821

Ancient batteries

Batteries have actually been around much longer than most people think. The first battery that we have proof of dates back to about 200 BC. This ”Bagdad battery” was discovered 1938 by archeologists in Khujut Rabu close to Bagdad. It consisted of a clay jar which contained an iron rod encased in a copper cylinder. This primeval battery was able to deliver a potential of 1.1 V when the jar was filled with vinegar as the electrolyte. Though there are no written records about their application, scientists assume that they were used to electroplate items, i.e. to put gold coatings on metal objects.

The Voltaic Pile

We have to fast-forward to the year 1800 to find the next historic battery, the ”Voltaic pile”. It was developed by Alessandro Volta in Italy and consisted of alternately stacked zinc and silver discs. In between the discs Volta placed cardboard soaked in salt water. When a wire was connected from the bottom zinc to the top silver disc it could produce sparks. Another discovery we have to thank Volta for is the electrochemical series which arranges metals according to the potential they can deliver against a standard electrode.

The Daniell Cell

The next step was taken by the British researcher John Frederich Daniell who developed the Daniell cell around 1820 which could deliver more stable currents than the voltaic pile. It consisted of a zinc plate and a copper plate that were placed in separate vessels filled with a liquid electrolyte. A salt bridge was added between the two vessels and a potential of about 1.1 V could be delivered. The Daniell cell was used to power, e.g. telegraphs and telephones for over 100 years.

The Lead Acid Battery

In 1859 French physicist Gaston Planté started experimenting on what would later be known as the lead acid battery, also being the first rechargeable battery. It consisted of two rolled-up lead sheets with a piece of flannel placed in between them. This assembly was immersed into dilute sulphuric acid. Many improvements have been made since then to reduce the amount of liquid acid in the battery, but their working principle has not changed. They are still widely used today, for example as car batteries.

The Leclanché Cell

French scientist Georges Leclanché developed a smaller and lighter, but non-rechargeable, battery in 1866, the Leclanché cell. It was made up from zinc, manganese oxide mixed with carbon and an ammonium chloride electrolyte. These cells were widely used for almost 100 years until they had to give way for the newer alkaline-manganese batteries in the 1960s.

Nickel-Based Batteries

From 1893 to 1909 the nickel-cadmium battery was developed as a rechargeable cell in Sweden by Waldemar Jungner. These efforts were similar to work carried out by Thomas Edison in the USA around the same time. However, Edison`s nickel-iron battery failed quite spectacularly when it was employed to power cars. Jungner`s nickel-cadmium battery, on the other hand, is still widely used today based on the same chemistry he invented. In the 1970s the nickel-cadmium battery was refined and the nickel-metal hydride battery was created in Switzerland. The goal was to avoid the toxic metal cadmium in batteries. These cells can still occasionally be found in portable electronics today.

The Alkaline-Manganese Battery

The alkaline-manganese battery (or alkaline battery) was developed as a small, light and non-rechargeable cell in 1949 by the Canadian engineer Lewis Urry. It was based on the same chemistry as the Leclanché cell using zinc and manganese oxide. But the ammonium chloride electrolyte had been substituted with potassium hydroxide. These cells are the most popular non-rechargeable battery system today.

The Lithium-Ion Battery

The lithium-ion battery is probably the most reasearched battery system today. It was first introduced in 1991 by Sony after several seperate inventions of John Goodenough, Rachid Yazami and others. These batteries are the most energetic rechargeable batteries available and power almost all portable electronic devices like computers and mobile phones. Lithium-ion batteries are based on a rocking-chair-principle were lithium ions can be transported through an electrolyte between two electrodes. Common commercial electrode materials are graphite and lithium cobolt oxide or lithium manganese oxide. However, there is still a huge amount of research being carried out in order to find better materials.

Beyond Lithium-Ion Bateries

At the moment there is also a growing amount of research on new battery chemistries, which include the sodium-ion battery, magnesium-ion battery, potassium-ion battery and more. They normally orperate on the same rocking-chair-principle as lithium-ion batteries. The reason for this kind of research is that lithium is a very limited raw material, while other materials like sodium are much more abundant on Earth and therefore cheaper. It will be very interesting to find out if any of these batteries will be commercialized on a large scale in the future.

Some good news

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Climate change, extinction of species, de-forrestation, multi-resistent germs, chemical warfare and so on. The media – also science-based – is  full of bad news.

This is the reason I wanted to write about good news in science for a start. There are some good news out there, but we often fail to click on them and share them as often as we do with the bad ones.

So, here it comes, the good news of the day.

*Drum-roll*

Solar power is becoming cheaper than electricity generated from fossil fuels!

In the end of 2016, unsubsidized solar power projects have been able to outcompete coal and natural gas for the first time. And guess what? The cost for solar panels will continue to fall. Wind energy is becoming cheaper too, but at a lower speed.

This means investments in renewable energy projects are no longer only for Green Party members, but a real alternative for profit-orientated companies and billionaires. This can accelerate the expansion of solar and wind power plants. Especially developing countries could profit from this development to build and extend their national power grids. Here is another great aspect: Solar and wind power plants create more jobs than their fossil fuel counter parts!

Unlike coal and natural gas, oil will most likely not be replaced as quickly since airplanes and the vast majority of cars run on oil-derived fuels. It is also necessary to make products based on plastics. But if we eventually switch over to electric cars, most of our oil production could become redundant like coal and gas. This would leave us with cleaner air and quieter cities, not a bad prospect, is it?