The conventional lithium-ion battery packs currently used in our bicycles and also in electric cars are mature, and their development is largely exhausted, which is why research is now moving toward solid-state cells. Semi-solid-state cells are regarded as a transitional stage on the path to fully solid-state batteries. In contrast to lithium-ion cells, which rely entirely on liquid electrolytes, semi-solid-state cells use a semi-solid electrolyte intended to combine the advantages of liquid and solid systems.
In 2024, Chinese car manufacturer NIO announced the market launch of a battery pack with semi-solid-state cells from cell manufacturer WELION, which can be described as one of the world’s first semi-solid-state battery packs for electric vehicles. And this is where the enterprising ergetic Kalle from NICOLAI Bikes comes into play: with his company Universal Transmissions (UT), he offers battery modules with WELION Semi-Solid-State cells for E-Bikes. The production of the battery packs is planned to take place, among other locations, at EMBS in Gliwice, Poland.
Status quo: Round cells 18650 & 21700
Cylindrical lithium-ion round cells currently dominate the e-bike market. 18650 cells (18×65 mm) were once standard, but newer 21700 cells (21×70 mm) provide more volume—and with it, higher capacity and energy density.
Higher energy density means: the same range with fewer cells, or more range in the same space.
Pouch instead of cylindrical – WELION’s semi-solid-state cells
WELION use pouch formats for their semi-solid-state cells—flat “bag cells” easiest to visualize as a chocolate bar: multiple thin layers, efficiently stacked with minimal wasted volume in the housing The electrolyte is hybrid (partly solid, partly liquid): the goal is higher energy density, fast-charging capability, and improved safety compared to pure liquid electrolyte cells (such as lithium-ion cells).
Universal Transmissions use semi-solid-state cells supplied by WELION, available in two e-bike-specific versions: 20.3 Ah at 9 mm (71.3 Wh, SPH380-20) and 25.4 Ah at 11 mm (89 Wh, SPH380-25).
Pros and cons of a semi-solid-state battery compared to a conventional lithium-ion battery
Pros of semi-solid-state cells
- Increased energy density
- By partially incorporating solid electrolytes and packing the electrodes more densely, it is theoretically possible to achieve energy densities 20–50% higher than those of conventional lithium-ion cells.
- This means: more range with the same battery size.
- Better safety
- With the liquid electrolyte portion greatly reduced, the cells are less flammable, which in turn lowers the risk of fire or thermal runaway.
- Mechanically more stable than lithium-ion cells, since solid-like components can help prevent dendrite-induced short circuits.
- Higher charging speed (potentially)
- Lower internal resistance and better ion conductivity in certain designs can enable faster charging.
Challenges in using semi-solid-state cells
- Not yet fully matured
- The commercialization of these cells for e-bikes is still in its early stages; true mass production, as seen with lithium-ion cells, does not yet exist.
- Cost and scalability
- At present, materials and manufacturing costs are higher than those of conventional lithium-ion cells.
- Mass production is still ahead → the price per kWh is currently likely higher. However, the technology itself is not inherently more expensive, and costs are expected to be very similar—or even equal—once the same production volumes are reached.
Comparison of battery sizes from Avinox/Amflow, Bosch, Universal Transmissions-WELION, and Specialized
| Avinox (Amflow) 800 Wh |
Bosch PowerTube 800 Wh |
UT-WELION SHP380-20 |
UT-WELION SHP380-25 |
Specialized Turbo Levo 840 Wh |
|
|---|---|---|---|---|---|
| Rated capacity | 22.3 Ah | 22.2 AH | 20.3 Ah | 25.4 Ah | 15.99 Ah |
| System voltage | 36 V | 36 V | 35.1 V | 35.1 V | 50.96 V |
| Nominale Kapazität | 802,8 Wh | 799,2 Wh | 712,5 Wh | 891,5 Wh | 814,8 Wh |
| Weight kg | 3.796 | 3.932 | 3.109 | 3.624 | 4.396 |
| Dimensions mm | 561 x 71 x 49 | 424 x 77 x 71 | 422 x 76 x 64 | 422 x 76 x 72 | 408 x 70 x 85 |
| Battery density [Wh/kg] | 211.48 | 203.25 | 229.17 | 245.99 | 190.85 |
The above values come from Avinox/Amflow, Universal Transmissions-WELION, or were taken from our article Is the battery arms race in the eMTB sector fair?
A conventional 800 Wh e-bike battery consists of around 40 lithium-ion cylindrical cells. UT-WELION’s e-bike battery achieves a similar Wh rating (712 Wh and 891 Wh) with just 10 pouch cells. By using semi-solid-state cells instead of the previously standard lithium-ion cells, the weight of the battery can be reduced significantly.
The table clearly shows that semi-solid-state cells allow comparably sized batteries to achieve higher capacity while also reducing weight.
Questions for Kalle Nicolai
Kalle Nicolai is known as the founder of bike brand NICOLAI. Less well known is that in 2006, Kalle founded Universal Transmissions GmbH (UT) to independently develop and distribute gearbox and drive technology (including GBOXX) as an OEM supplier, separate from the NICOLAI bike brand. UT positions itself as a development and system partner for future-proof LEV products (Light Electric Vehicles) and is a distributor for Gates Carbon Drive and Bosch eBike Systems. In 2024, UT entered into a partnership with WELION (Beijing WeLion New Energy Technology Co., Ltd.). WELION is a Chinese battery manufacturer considered a pioneer in commercial semi-solid-state cells, including as a cell supplier for NIO’s 150-kWh pack. UT is the official distributor of WELION cells for e-mobility in the EU.
What led you to start exploring e-bike batteries as well?
As part of our development work for LEV products (light electric vehicles), we were looking for more powerful batteries than the conventional lithium-ion cells. That’s when we got in contact with the Chinese cell manufacturer.
Which technical features of the WELION semi-solid-state cells convinced you?
Even initial lab tests with very high current draw showed that the semi-solid-state cells barely heated up. Through this, we recognized just how much potential these cells have.
Where do you see clear advantages in everyday e-bike use?
With the same level of safety, these semi-solid-state cells provide higher range and faster charging speeds at lower weight.
Does the pouch form factor (“chocolate bar”) change your module design compared to cylindrical packs
No! Together with WELION, we developed a new pouch format, making the same or similar battery packs possible.
How do the costs of semi-solid-state modules currently compare with Li-ion packs, and at what production volume do you anticipate cost parity?
Once a major e-bike manufacturer adopts WELION cells and production volumes increase, costs are expected to reach parity.
What opportunities do you see from the UT-WELION partnership for European e-bike manufacturers?
European e-bike manufacturers now have the chance to keep pace with the development speed of Asian companies like DJI.
Which technical key figures are you aiming for?
Currently “best in class.” We expect the next significant development step in about 15 to 24 months.
Is the move to full solid-state cells foreseeable—or will semi-solid-state remain the next industry standard?
I expect the shift in the e-bike segment to be gradual. Solid-state cells will likely still include 2–3% liquid content in the future, influenced by regulatory requirements both in China and in Europe.
When will a NICOLAI e-bike with a semi-solid-state battery hit the market?
The gentleman enjoys and remains silent!
When can E-MOUNTAINBIKE magazine expect a test bike with a semi-solid-state battery?
Not in the coming 12 months, but afterwards — we’re already speaking with several manufacturers.
Kalle Nicolai was technically supported during the interview by his CTO, Sebastian Braun.
Conclusions
“Semi” rarely sounds like progress—but for e-bikes, it could actually be the next big thing. Semi-solid-state battery technology promises more range, lower weight, faster charging, and at least the same level of safety as current Li-ion batteries—at similar prices. This brings a full-power e-bike under 20 kg within reach. How does this new battery generation perform in real-world riding conditions? Of course, you’ll find out here first.
Words: Manne Schmitt Photos: Manne Schmitt, diverse
