EMTB: Prof. Bohlen, for bikers, the achievable altitude metres are an important criterion.
Why not install much larger batteries in an e-mountainbike today?
BOHLEN: Technically nothing. It's a question of appearance, weight and cost. However, the pure cell accounts for less than half of the battery costs. The rest is in the housing, electronics, development costs and marketing. If you only calculate the battery cells alone, you can already get the cells for a 500-watt battery for less than 100 euros. And the price drop is currently enormous.
Size and weight: the more energy, the larger and heavier the battery?
The size would not be the problem. There is generally enough space in the frame triangle for a battery twice the size. But two kilos more for a battery twice as powerful - that certainly makes a difference in terms of handling. In terms of weight, however, I still see room for manoeuvre in the future. Batteries can become lighter.
What does the weight saving depend on?
In today's lithium-ion battery, there are only around two grams of lithium ions in a cell that weighs just under 50 grams. Weight could therefore still be saved on the periphery around the lithium. Lithium-ion batteries currently use graphite and metal oxides as electrodes, which is quite heavy. Work is being done to find something lighter. There is also the idea of a lithium-sulphur battery, or a lithium-air battery, in which one electrode is made of normal air.
And why lithium at all?
It is the lightest metal in the chemical periodic table, the first element that is not gaseous at room temperature, such as hydrogen and helium. However, lithium is not contained in the batteries as a metal, but as ions in a carrier, a solvent. This results in the so-called electrolyte. Today, it is usually absorbed into the battery like a sponge or gel, so that you can no longer hear it gurgling.
Some see the fuel cell as the energy supplier of the future.
We already have fuel cells that could be used to drive thousands of kilometres. However, this is a very complicated technological field - you have to compress hydrogen, you need a pressurised tank and a cooling system. Direct methanol fuel cells are somewhat easier to operate, but are less efficient and are not an alternative for e-bikes in the foreseeable future.
What does an e-bike battery look like on the inside?
These are individual battery cells, usually three to five in parallel and then ten to fourteen such packs connected in series.
Wait, what is the difference between series and parallel connection?
Connected in series means that the positive terminal of one cell is connected to the negative terminal of the next cell. This increases the voltage from cell to cell. If a cell has a nominal voltage of around 3.6 volts, then ten cells connected in series will produce 36 volts. Connected in parallel means that two or three cells are installed next to each other in order to increase the amount of charge or energy. If, for example, a pack without parallel connection has 100 watt hours, then three parallel packs will achieve 300 watt hours.
How quickly will the technologies develop?
Lithium-ion batteries will almost certainly remain the dominant technology for the next five to ten years. There will always be smaller steps in terms of energy density, efficiency and weight. However, I don't yet see a real technological breakthrough in this period that would make batteries more than 50 per cent more powerful. So until then, we can probably expect about 50 per cent more range with the same size. Only after that will we see the lithium-sulphur or lithium-
air battery or even the fuel cell for e-bikes. We are dealing with chemical elements whose properties we already know today. So there won't be a rapid development like that of computers, for example, where computing power has increased a thousandfold in a few years. But the pressure from industry is of course great, especially due to the boom in portable devices such as laptops, smartphones and now e-mobility.
What can e-bikers do today to keep their battery performing for as long as possible?
Overcharging, deep discharging and high temperatures damage the battery. It should be recharged with a good charger as soon as possible after the journey. If you don't use it for a long time over the winter, for example, you should make sure that it is not empty and it is better to store it in a cool cellar than in a warm living room.
