Lithium or lead batteries

Interview

Mr. Ruscher, lithium-ion energy storage systems are sweeping the market. Is that the end of the lead-acid battery?
Well, as we know, the dead live longest. But seriously, the now wide selection of Li-ion batteries for industrial applications, such as an uninterruptible power supply, may be pleasing, but it is still a long way from being the swansong of the lead-acid battery. At the moment, the two technologies only overlap in some areas, and it is still necessary to take a close look at the applications.

But doesn't the new generation of Li-ion batteries have significant advantages in terms of energy density, service life and temperature stability?
Yes, that's true if you look at the values themselves. Don't get me wrong, modern Li-ion energy storage systems are providing much-needed impetus for innovation in the field of uninterruptible power supplies. We would be a bad manufacturer if we didn't evaluate this technology carefully and incorporate it into current products. If they have the right application, the key data of Li-ion batteries cannot be beaten.

What could such an application be?
It's about the application, not just the application itself. Depending on the application, a UPS in a data center can be optimally operated with lead or Li-ion. For example, a data center can be set up in a very cramped building where every square meter of space is very expensive. Li-ion has advantages there because the energy density is higher. In addition, Li-ion does not require its own ventilated battery room due to the absence of outgassing. This also saves space and therefore costs. However, if space requirements are not an issue, lead-acid batteries are often the better choice for data centers.

Are there other applications in which Li-ion is ahead?
I think that, in addition to the higher energy density, the cycle stability is the second major advantage of Li-ion. It is at least 10 times higher than that of a standard lead-acid battery. This is always important when the voltage frequently falls outside the tolerance range and the UPS has to buffer. You will find such situations in countries with less mature power grids. Or if there is a lot of construction in a region and the grid supply is frequently disconnected. The entire home grid sector also places high demands on cycle stability. Here, a battery is charged and discharged daily.
However, there are also special industrial applications that can be operated significantly better and more efficiently with Li-ion than with lead. For example, we offer UPS systems for use in peak shaving. This involves intercepting load peaks that would otherwise lead to increased supply charges from the electricity supplier. Such peaks usually occur on a daily basis, which means that a lead-acid battery very soon reaches the end of its service life. Li-ion batteries, on the other hand, last much longer and therefore require less maintenance and, viewed over their entire service life, incur lower overall costs.

Keyword costs. In comparison with lead-acid batteries, the higher costs of Li-ion have always been mentioned. Are the two technologies gradually converging in this respect?
So, the purchase price of a Li-ion battery is higher than that of a lead-acid battery, and will remain so for the foreseeable future. But that does not mean that the resulting solution is more expensive, especially not in terms of service life. As already mentioned, the service life of Li-ion batteries is significantly longer than that of comparable lead batteries. Even if pure lead batteries with a theoretical service life of 15 years are used, the achievable service life is significantly lower. And this applies to optimum conditions in terms of temperature and charging cycles. A Li-ion battery is more moderate in terms of temperature requirements and the consequences for the service life are significantly lower. It significantly changes the cost structure of the solution if the energy storage units remain optimally usable for longer.

So it only makes sense to consider the costs over the entire service life of the solution?
Yes, absolutely. And you must not forget that a battery management system is always built into a Li-ion battery. There is no other way, because the cells are much more sensitive to overcharging. The BMS ensures that optimum conditions prevail for the cell at all times. In addition, the BMS provides a wide range of very important data, for example to intervene proactively if parameters deteriorate. Although BMSs are also available for lead batteries, they are almost never installed. This means that a comparison of the two battery technologies at the level of the individual cells is not meaningful in terms of costs anyway.

As you have just mentioned, the issue of safety plays a completely different role with Li-ion batteries than with lead. The risk potential is considered to be significantly higher. Is that still the case?
Yes and no. First of all, we need to take a more differentiated look at lithium-ion technology. So far, we have always talked about Li-ion without going into the actual materials used. Lithium is often combined with manganese as the cathode. This results in relatively light cells, which are also used in the automotive sector. However, their disadvantage is a violent reaction when damaged. Iron phosphate, on the other hand, has very similar storage properties with a slightly higher weight, but reacts much less aggressively when damaged. Even if a nail test is not absolutely conclusive, it does show how differently the two material combinations react.

In the nail test, the cell wall is penetrated with a steel nail?
Correct. And in contrast to lithium-manganese cells, which practically always react with smoke and flames during the nail test, lithium iron phosphate only emits gases.

Does this mean that there will soon be a VDS approval for lithium-ion cells?
I am absolutely of the opinion that the manufacturers of Li-ion blocks should strive for such certification. But in my opinion, you shouldn't expect approval any time soon, as the effort involved is very high.

Even if the service life of Li-ion cells is very long compared to a lead-acid battery, at some point they will reach the end of their service life. And then, as many critics say, it looks bad when it comes to recycling.
At the moment, recycling lead batteries is much easier, of course. But that's because we have many years of experience with it; lead batteries have been recycled for half a century. And even with lead, it took a long time for an economically viable recycling model to emerge. With Li-ion, we don't have the experience, the infrastructure and the entire ecosystem, which is currently being created. But it is also clear that Li-ion cells are so valuable that we cannot afford to do without recycling them. That is why there will also be functioning recycling models.

They paint a mixed picture of Li-ion technology. Technically superior, but not always, more expensive, but not in terms of overall service life, safe if the right mix of materials is used. In your opinion, what does the future of energy storage look like in concrete terms?
I would rather use the term "application-based" instead of "mixed". If you have a suitable application, Li-ion is the perfect technology, even today. Li-ion is market-ready and available, not only do we offer solutions with Li-ion, other manufacturers do too. To find out whether lead or Li-ion is the right energy storage system, you need to know and analyze your application in detail, preferably together with a partner who knows exactly what is feasible and at what cost. You will be surprised how often the economics speak in favor of lithium-ion technology.

Dietmar Ruscher, authorized signatory at Wöhrle Stromversorgungssysteme GmbH, has been with Wöhrle for over 30 years and held the position of technical manager until April 2020. After handing over this position to his successor Mr. Markus Steiner, he will continue to support Wöhrle and its customers with his many years of experience and expertise.