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Saft Li-ion batteries in space

In the week where 27 of its lithium ion cells were launched into space aboard a European satellite, Electronics Weekly talks to French firm Saft about batteries in space.

The VES 100 cells went up aboard Giove-B, the second experimental satellite in Galileo – Europe’s answer to GPS – and will provide 600W through eclipses of up to 60 minutes at least 170 times a year.

A bit of history

NiCds were the original rechargeable space battery, gradually superseded by pressurised NiH2 types in the 1980s and 90s.

In 1998, UK firm ABSL Space Products, qualified a Sony 18650-size Li-ion cell for space use.

Then known as AEA Technology Space, it had invented Li-ion cathodes and licensed them to Sony.

This cell was launched on the UK military spacecraft STRV-1c in 2000, followed over the next few years by flights on NASA and ESA spacecraft.

Advantages

The big advantage is weight, with Li-ion cells significantly lighter than their nickel counterparts, but there are two other significant benefits.

“Efficiency of recharge is high so they don’t heat up,” Antoine Brenier, business development manager at Saft Specialty Battery Group told Electronics Weekly. “If they don’t heat up, they don’t need cooling down, so you save on radiator mass.”

The other is that they keep their charge, loosing only five per cent per year, whereas NiH2 cells rapidly self-discharge. “If the launch is delayed, you don’t have to plug the launcher into the launch pad like you do for NiH2,” said Brenier. “So the satellite and launcher need no power wiring for charging.”

Insurance

Deciding what battery chemistry to put in a satellite is not simply a technical decision. It is also about insurance as insuring a payload is incredibly expensive and complex.

“Track record is important in space. The younger the battery, the higher the insurance,” said Brenier. “The track record is measured in the number of years installed capacity has been in space, or the number of cell-years. We have a total of 240kWhr of Li-ion in orbit, with the first going up in March 2004 in W3A, a communications satellite.”

Getting insurance for the crucial first launch requires some help. “It is no secret that, to make some life tests lasting years, we got support from ESA (European Space Agency) and from the French division of ESA,” said Brenier.

Technology

Between them, Saft in France, ABSL in the UK (using Sony cells) and Mitsubishi Electric of Japan provide all the Li-ion cells that go into space, with US NiH2 space battery firm Eagle Picher shipping its first Li-ion space batteries (using GS-Yuasa cells) to satellite maker Orbital Sciences late last year.

The cells are made from the same materials that go into laptop and phone batteries. “The electrochemical recipe is fine-tuned for space,” said Brenier.

However, the construction is more robust. “At the beginning of their life they are going through launch with vibration and shock for about 20 minutes,” said Brenier.

Two other differences make space batteries last for 15 years in space instead of the three they survive in consumer products: production quality and electrical environment.

“There is very very strict and thorough quality control at each step of manufacture, starting from the material with which we coat the electrodes,” said Brenier. “Then, we manufacture a number of cells and send only the best to customers. We cycle them at different temperatures and the customers also make some tests.” Cells are also selected for balance within a battery.

In laptops and phones, a nominal 100 per cent of cell capacity is used – charging to 4.2V/cell for extended periods and discharging down to 2.75V, or even 2.5V to extract maximum energy.
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