Tesla's Battery Day on Tuesday was one of the most highly anticipated moments of the tech calendar, and Elon Musk used it to lay out his vision for more sustainable technologies, in-house battery production and, most interestingly, huge advances in battery technology.
In front of an audience sitting in Tesla cars and hundreds of thousands watching online, Musk announced that new battery technologies that would mean his electric vehicles will be more powerful, longer lasting, and less expensive. What this boils down to is Tesla being able to sell a full electric car for $25,000 USD within 3 years.
It's impressive stuff, but will we ever see this technology in eMTBs, and what will it mean for their development? First, let's take a look at the batteries that we use now.What is inside an eMTB battery?
At the moment most eMTB batteries are 18650 Lithium-ion (Li-ion). Li-ion batteries were first developed in 1985 and they have been the main driving force behind electric vehicle development as they are rechargeable and you can get a lot of power from them without them taking up too much space.
The 18650 part refers to the cells within the battery pack. Each battery is packed full of individual cells that measure 18mm x 65mm, roughly the size of your finger. These are welded together in packs that are connected in parallel. If you take off the plastic shell, it basically it looks a bit like a bunch of AA batteries all joined together.
What goes on inside the battery isn't that important, but there is one important number with batteries - watt-hours. This, like you might expect, is a measure how many watts can be delivered in an hour. So for example, a 250 watt-hour battery could drive a 250 watt motor on full power for one hour while a 500 watt-hour battery could drive it for 2. Most e-bike batteries sit between 300 and 550 watt-hours. The golden bullet with batteries is getting as many watt-hours as possible, but if you just keep adding cells you'll start adding weight and volume.
Tesla doesn't currently use 18650 cells, though; it now uses the 21700 standard with cells measuring 21mm by 70mm. Tesla developed this cell with Panasonic in 2017 and its larger volume means it can be packed with more anodes and cathodes so can hold more energy. Tesla also claims it has a longer lifespan as it has to be charged less.
We have recently started to see these cells come into eMTBs with Specialized's Turbo Levo Kenevo
being the one we have covered the most on Pinkbike. This bike has a massive 700Wh battery, making it one of the biggest you can get on an eMTB today.
Tesla hasn't stopped 21700 though, and its announcement on Tuesday is the next evolution of its cell technologyHow is Tesla's New Battery Different?
The new Tesla battery has gone up in size again, this time far more significantly to 4680 or 46mm x 80mm. However, the real innovation comes from what's inside the can. Both 18650 and 21700 standard cells use 2 tabs connected to thin bits of copper and aluminum foil to connect the workings of the battery to the outside world. Not only are these tabs complicated to manufacture but they also take up space inside the battery and reduce efficiency as the current must travel the full length of the electrode to reach each tab.
Tesla's new design gets rid of these tabs and instead uses a "shingled spiral" design to collect the current which reduces internal resistance, reduces cost and simplifies manufacturing. Musk said: “The distance the electron has to travel is much less. So you actually have a shorter path length in a large, tabless cell, then you have in a smaller cell with tabs. So even though the cell is bigger, it actually has a better power-to-weight ratio.”
According to Drew Baglino, the senior vice president of powertrain and engineering at Tesla, the innovations boost the energy by five times, the power by six times, and the range of a car using these batteries by 16 percent. It's worth saying we don't know what the baseline for these numbers are as no exact figures are given but we assume its in relation to the 21700.Will we ever see this on eMTBs?
The advantages for eMTBs of a more powerful battery are clear. You can either deliver the same power in a smaller, lighter package, therefore making the bike handle and look more like a traditional mountain bike, or you can keep the battery the same size and boost the range of the bike.
As impressive as Musk's claims were, there was one problem. While the cells are apparently currently in testing, a physical one wasn't shown and it will apparently be another three years before the technology is released. Don't expect to see eMTBs using them straight away either. It took roughly 2 years for the 21700 tech to trickle down from Tesla Model 3 cars to the Specialized Kenevo, so you can probably expect tabless batteries to be the same, if it even happens at all.
There are also reasons that bike manufacturers are currently satisfied with the 18650 system and don't see any reason to change. There is still plenty of innovation in this size of cell with Bosch unveiling its 625Wh Powertube battery last year, offering a huge range despite the smaller cell size. The internals of these cells are still being perfected too with engineers experimenting with different cathode and anode materials to boost capacity.
One of the other big problems of increasing the volume of a cell is that it makes it harder for heat to escape. If a battery gets too hot it has to operate at reduced power or risk damaging itself permanently. E-MTBs are often out in the sun all day so the better heat management of an 18650 cell could lead to better performance over a longer period of time.
Finally, as with all things, cost will surely be a factor. 18650 cells are well proven technology, have now been refined for cycling applications and are widely produced by a number of competing brands. New technology is rarely cheap, especially in its infancy and while Musk is targeting a $25,000 USD electric car, we doubt he will let that competitive advantage go easily.
So, will eMTB batteries get smaller, lighter, cheaper and more powerful? Almost certainly. Will that be because of Elon Musk? Probably not for a while at least.