46xx cylindrical cells is an abbreviation for the new class of 46mm diameter cells.
The Tesla 4680 cell is 5x the energy of the 21700 cell.
Perhaps the most important upgrade is not the larger cell, but the change to the engineering design and the manufacture of this cell.
The tabless jelly roll significantly improves the electrical and thermal connections. Tranter et al have analysed this design and looked at the electrochemical and thermal behaviour.
The new design is found to mitigate the ohmic losses experienced around the “jelly-roll” current collectors which are significant for the traditional tabbed case, thus leading to higher efficiency and capacity and reduced heat production.
T. G. Tranter, R. Timms, P. R. Shearing and D. J. L. Brett, “Communication—Prediction of Thermal Issues for Larger Format 4680 Cylindrical Cells and Their Mitigation with Enhanced Current Collection“, Journal of The Electrochemical Society, Volume 167, Number 16
Next to move to a 46mm diameter cell is perhaps BMW. However, they have grown the height of the cell.
The BMW Gen6 battery is also a push to lower costs and improved energy density. Initially the cells will have NMC chemistry and will be manufactured by BMW’s existing partners CATL and EVE.
The BMW goals are:
- lower cost
- improve energy density
- reduce charging time
- reduced manufacturing emissions
BYD have produced an LFP chemistry in the 4680 cylindrical format. The cell is designated FC4680P and has a nominal capacity of 15Ah. Also, note that this cell has an “explosion proof valve”.
Fraunhofer [1] have looked at the cell format and from this predicted the capacity different chemistries can achieve. We have used these values and added a line for the first Tesla 4680 cell.
| Chemistry | Nominal Voltage [V] | Capacity [Ah] | Vol. Energy Density [Wh/litre] | Grav. Energy Density [Wh/kg] |
| LFP / Graphite | 3.2 | 19 | 450-470 | 170-180 BYD FC4680 = 129 |
| LMFP / Graphite (Mn 50%) | 3.55 | 18-19 | 500-520 | 185-195 |
| NMC811 / Graphite (Tesla 4680 gen 1) | 3.7 | 23.4 | 650 | 244 |
| NMCA / SiNP/Graphite composite | 3.45 | 31 | 800-820 | 285-290 |
| NMCA / SiMP (limited voltage) | 3.3 | 31 | 765-780 | 275-280 |
| NMCA / Si | 3.35 | 34 | 860-880 | 305-310 |
Can the 46xx cell be improved by moving to an aluminium casing?
Aluminium Cell Housings for Cylindrical Lithium-ion Batteries
Thermal simulations reveal significant improvements in cooling performance at 3C fast-charging of the aluminium housing version compared to nickel-plated steel reference cell. The impact of the cell housing material is particularly pronounced in case of a sidewall cooling. In this case, simulation reveals differences in maximum temperature (hot spot) of 11°C after 10 minutes.
Aluminium 4680 Cell Can Structural Performance
A look at the structural performance of aluminium 4680 cell cans made from two different materials namely Speira ION Cell 3-CB and Speira ION Cell 3-CS will be presented. The cell cans were produced by deep-drawing and wall-ironing featuring a wall-thickness of 0.75 mm. The can bottom features a thickness of 0.9 mm. The deep-drawing and wall-ironing route allows the application of high strength aluminium alloys and hard tempers.
References
- Potentials of 46 mm cylindrical cells: On the way to the new standard format, Fraunhofer ISI
- T. G. Tranter, R. Timms, P. R. Shearing and D. J. L. Brett, “Communication—Prediction of Thermal Issues for Larger Format 4680 Cylindrical Cells and Their Mitigation with Enhanced Current Collection“, Journal of The Electrochemical Society, Volume 167, Number 16