E-MTB Battery Revolution? A realistic Assessment of the Situation
Who doesn’t dream of a long-lasting battery that charges within seconds when required? Articles about sensational breakthroughs in the development of super-batteries and mega-cells are popping up like mushrooms on the web. But are these just rumors? We interviewed four industry gurus to find out.
Sven Bauer
Founder und CEO BMZ Group
What’s the current state of affairs, where are we today, and what are the biggest challenges in the development process of new battery technologies and cells?
The technology of bike batteries is changing. They’re getting smaller and lighter and can offer a bigger range and a longer lifespan. The older 18650 cell dimensions are a thing of the past, and we are turning the page with the 21700 cell type.
This is exactly the same automotive cell Tesla are using for their cars. It brings more performance, a bigger range, and a lower weight; it’s a new generation of batteries that is also revolutionising the bike market. This will make it easier to integrate batteries into bike frames, allow for extended warranty terms for the end-consumer, and obviously increase the battery range.
Can we expect major developments with regards to battery capacity for e-bikes in the foreseeable future (over the next two years)?
This is a very technical topic, but I’ll try to explain it. In the past we were mainly using the NMC type for bicycles; that’s nickel, manganese, and cobalt on the cathode and graphite on the anode. We have now moved on from this technology and are using the NCA type, which is a nickel-cobalt-aluminium type; this means a 30% increase in volume- and weight-capacity and also results in a 30% range increase or a battery that is 30% smaller and lighter.
At the same time, we replaced the graphite on the anode with silicon, which also results in an increase in capacity. To put it simply — the same way it happened for mobile phones — the battery disappears inside the frame and is no longer visible, and at the same time you will be able to ride long distances. Thanks to the 21700 cell size we will soon be witnessing a giant leap in the e-bike market. This will allow us to give customers longer warranties whilst the battery will no longer be visible. In addition, the battery range will be extended. BMZ is developing special cells exactly for this purpose which will be available on a number of bikes over the next few years.
Ingo Beutner
Head of Engineering Haibike
What’s the current state of affairs, where are we today, and what are the biggest challenges in the development process of new battery technologies and cells?
Can we expect major developments with regards to battery capacity for e-bikes in the foreseeable future (over the next two years)?
I’ll try to reply to both questions with one answer. Currently all bikes and system manufacturers are using cylindrical cells, which are combined with a BMS (Battery Management System) and are placed inside a housing. Even a global player like Tesla, who can certainly count on totally different levels of financial possibilities, relies on such cells for its electric car production.
The most common cell is the 18650 cell (18 mm diameter, 65 mm length). The 21700 cell (21 mm diameter, 70 mm length) was recently added, but it’s still somewhat exotic for the international market (also considering that long-term data is not yet available). Because Tesla will be using this cell for their future car models, research and development will benefit from this move.
All batteries are based on the laws of chemistry. In the charging process, potential differences are generated using the relevant substances (i.e. lithium), then stored and released again if necessary. But there are different ways for cells to do this: for power tools you’ll need high discharge currents to ensure high performance in a short time. On the other hand, for other applications you’ll need a high storage capacity.
Both things are slightly different from each other and – especially when it comes to e-bikes – we have to take thermal aspects into account.
At the peak of summer, a battery can easily reach temperatures of over 60 °C! At this point the BMS would automatically reduce the battery’s performance to avoid overheating of the cells and prevent permanent damage.
There is a specific cell for every type of application, and e-bikes are no exception. New technologies try to optimize cells for their intended application. The main focus is on the chemistry of substances in order to squeeze out every ounce of performance.
However, it is just as important to reach a high production quality, because each battery will only be as good as the worst cell in it! If a cell producer can raise production quality, the whole battery will automatically be better.
Let’s also keep in mind that these improvements are only gradually achievable, and by no means will we experience a doubling in storage capacity within one to two years! “Wonder batteries” like the ones we come across in Facebook articles or news pages are usually just experiments and projects of universities and mostly optimised for a very specific field of application (i.e. a mobile phone battery with 2,000 mWh). For certain benchmarks, extremely high-charging currents are used to “pump up” a battery within seconds or minutes whilst all components are cooled down with liquid nitrogen. This is a scenario which is still totally unthinkable in an everyday application, and light-years away from any sort of serial production!
However, such experiments can open doors to new technologies we couldn’t even think of before. Short term (two to three years) not much will change as far as development of e-bike batteries goes, and even cells will only get slightly better for the same reasons mentioned above. In addition, we have to consider that new battery cells and/or system manufacturers have to go through a strict certification process and multiple tests before a serial product can be produced! Let’s suppose there will be a slightly better cell available on the cell market next year – we’ll still have to wait another one or to two years before this cell can even be used inside a battery.
The one thing I can actually foresee for the next two or three years is an improvement in capacity! Range will always remain a hot topic, and an extra 3 kg for a larger battery or a range-extender will be accepted as a welcome solution if these systems can provide twice the action range.
For upper-middle range or high-end e-bikes I can see 600 Wh batteries becoming a standard option in the near future.
Jan Talavasek
Specialized E-Mountainbike Engineering Manager
What’s the current state of affairs, where are we today, and what are the biggest challenges in the development process of new battery technologies and cells?
As far as energy density goes we have reached a plateau. Loads of new, different cell technologies are being developed, but nothing concrete will be available anytime soon – not even in two years’ time! It’s not just about energy density, but also output density, longevity, high/low temperature behaviour, and last but not least, safety. Small improvements in a 10% to 20% range will continue to be achieved annually, but the miracle cell will still remain a distant fantasy.
Can we expect major developments with regards to battery capacity for e-bikes in the foreseeable future (over the next two years)?
Right now we have to learn to manage the existing available energy in more efficient ways. Too small a battery is often not the real issue, but the fact that we “accidentally” waste a lot of the power without actually needing it. Smart software solutions will be required. With our Mission Control app and its SmartControl feature it is already possible to let the software control the motor support by setting a predefined target input; this way the charge will last until the end of the ride!
Tamara Winograd
Bosch eBike Systems Head of Marketing and Communication
What’s the current state of affairs, where are we today, and what are the biggest challenges in the development process of new battery technologies and cells?
Batteries play a crucial role as the source of energy in our Bosch eBike system.
It is generally true that energy density and the capacity of e-bike batteries have exponentially improved in recent years. Bosch e-bike batteries reach the best possible range due to a long lifespan and short charging time. The PowerPack 500 is one of the lightest batteries in its weight class and has the highest energy density.
The real challenge in battery development is reaching high capacity whilst keeping the battery as small and light as possible. System integration also plays an important role: the design of e-bikes is slowly getting closer to traditional bike designs. That’s why we need frame-integrated batteries. With the PowerTube 500 we are introducing a solution for our 2018 models: this new integrated battery combines modern design and high-quality Bosch technology for e-bikes with a clean and timeless look.
Can we expect major developments with regards to battery capacity for e-bikes in the foreseeable future (over the next two years)?
At Bosch we already have a number of proven e-bike batteries in our portfolio: they are light and small and offer a good range.
Depending on riding style and external conditions, an e-bike can reach ranges of up to 100km with one of the current Bosch drive systems.
We’ll continue to develop this sophisticated technology over the years to come. There are different scenarios: batteries with higher capacity at the same weight, or batteries with the same capacity but with lower weight and higher energy density. At Bosch we think in multiple and different directions. There is only one thing that doesn’t make sense: introducing new models every year. In the view of Bosch eBike Systems, progress only justifies the launch of a new product every two to three years.
Until then we can offer all e-bikers in need of more capacity our DualBattery, which is already an optimal alternative: a combination of two PowerPacks which offer up to 1,000 Wh, a great solution for long distances, long tours, and steep climbs.
Conclusion
Let’s be clear: the super-cell we often come across on the net won’t be available any time soon, but progress in the battery-technology field is tangible. On the one hand, the larger 21700-cell will probably increase battery capacity, on the other the work of companies like the BMZ group will hopefully soon allow us to ride farther and higher with a same-sized battery.
Apart from sheer capacity, aspects like longevity, performance, temperature-behaviour, and safety play crucial roles inside an e-mountain bike battery and also present great challenges during the development process. And of course, there is the price! New technologies aren’t usually cheap, and will be only seen on high-end bikes in the near future. If you’re planning to buy a bike you shouldn’t postpone your purchase waiting for some supposed new super-cell battery, but just go for it and enjoy the summer!
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