Daniel Porter
Mar 9, 2012

German scientists research batteries to surmount solar and lithium-ion limitations

Ruhr University Bochum Semiconductor and Energy Conversion Group

March marks the launch of an important German research group's project to build a better battery for storing energy produced from clean sources. The young group of electrochemical researchers at Ruhr University Bochum, one of Germany's largest research universities, has secured nearly €1.5 million in government money to work towards developing an aqueous lithium-ion battery. This project is the type of focused research effort that will likely spur a significant advancement in our current thinking about the clean energy problem.

Ruhr University Bochum Semiconductor and Energy Conversion Group

The RUB group hopes to change the way we think about lithium-ion batteries by searching for a new combination of electrochemical solution and electrodes. The goal is to devise a new battery cost-effective and safe enough for use in large-scale power supply systems that could eventually rely heavily on renewable energy.

According to the US Energy Information Administration, in 2011 renewables accounted for less than 15% of America's energy production, with solar representing an even smaller percentage. This is largely due to the fact that, despite the optimistic prospects that solar energy will play a central part in the global solution to the energy crisis, renewable energies still face numerous obstacles to widespread adoption. Chief among the handful of seemingly insurmountable problems that many renewables face is the intermittent nature of their power generation capabilities. Solar energy is by far the most prominent example. Even within the equatorial band that receives the most sunlight, diurnal and seasonal fluctuations mean that solar power is not always there when you need it. Solving this problem means storage, and our current technological options are surprisingly ill-suited to this end.

When it comes to storing electricity, batteries are used ubiquitously in applications from personal electronics to cars. The lithium-ion battery is the most modern incarnation of the rechargeable electrochemical cell, which fundamentally involve two metal electrodes submerged in a chemical solution. When connected to a charging current, the electrodes convert electrical energy into chemical energy stored in the solution, which can later be converted back for use in electrical circuits. Lithium-ion batteries represent more than half of all rechargeable batteries in use today, and the odds are good that your cell phone and laptop computer are both using Li-ion batteries because they are relatively safe, light, and long-lasting. The problem is that they don't scale. Batteries only really work well for applications that involve small cells and small amounts of current; at the end of the day, we still plug our smart phones and electric cars back into an electricity grid that relies heavily on the combustion of fossil fuels to generate a consistent supply of high-current electricity.

Large-scale Li-ion cells have problems of high internal resistance, rapidly decreasing the lifetime and inherent safety of the cells. So we are forced to keep cells small, which keeps manufacturing and maintenance costs high. Sure, they work well in consumer electronics, but electric car manufacturers have consistently struggled to find a affordable means of scaling battery implementations large enough to power a car. This doesn't bode well for our current technology's ability to store enough electricity to power a house, let alone a small community or a city the size of Los Angeles or New York.

The past decade has seen a significant increase in research time and money devoted to the development of renewable energy, in particular from the earth's most powerful energy resource, the sun. With all this focus, the global research community seems poised for a breakthrough that will change the way we think about getting energy from the sun. The first major problem is efficiency, as photovoltaic cells, arguably the most 'direct' means of producing electricity from the sun, harness no more than a quarter of impinging solar energy. Developments in this area show promise, especially with the success of solar concentrators and the potential improvements offered by nanotechnology, but there has been no revolutionary change in recent history. The second major issue is space -- because there is only so much sunlight that falls on any given square foot of earth, solar installations will inherently have to cover a large area of the earth's surface to accommodate our energy needs. Though the required area is only a small percentage of the global surface area, this currently means that solar installations are best placed far away from areas of high population densities, which calls for development of better transportation solutions.

Significant technological breakthroughs solving either of these problems will likely be necessary for solar to become the world's main power source, but neither is likely to address the third problem of intermittent sunlight. No matter how good solar power generation becomes, we need to store energy for use at night, or when the weather is cloudy, or in the winter when the average sunlight intensity can be less than half the summertime values. In the end we will need dramatically better batteries. If this improvement is going to come from re-thinking familiar electrochemical cells, the RUB group could very well be on the forefront. I, for one, am eager to see what they come up with.