The cell to pack mass ratio is a simple metric to calculate and gives you an idea as to the efficiency of your pack design.
This is simply the total mass of the cells divided by the mass of the complete battery pack expressed as a percentage. The larger the percentage the better:
- 84% (197 / 235kg) BMW i3 2013
- 76% (211 / 278kg) BMW i3 2018
- 75% (193 / 256kg) BMW i3 2016
- 72% (79.5 / 110kg) Ducati V21L Moto E 2023
- 69% (331 / 477kg) Kia EV6 2022 / Ioniq 5 2023
- 68% ( 224.64 kg / 332 kg) Tata Nexon Max (LFP)
- 63.5% (304.7 / 480kg) Tesla Model 3 AWD Long Range
- 62.9% is dataset average (see below)
- 61.0% (234.9 / 385kg) Formula E Gen 2
- 59.8% (191.4 / 320kg) Formula E Gen 1
- 59% (185.5 / 315kg) 2015 Nissan Leaf (30kWh)
- 59% (784 / 1326kg) 2021 GMC Hummer EV (212kWh)
- 57.9% (175.5 / 303kg) 2018 Nissan Leaf (40kWh)
- 52% (39.2 / 75kg) Koenigsegg Regara (4.5kWh)
An interesting benchmark, but there are some things to note as general guidance:
- Larger battery packs will have a better ratio as some of the overheads are fixed (eg contactors, fuses)
- Passively cooled packs should have a better mass ratio, however, the Nissan Leaf proves this wrong.
- Packs should include coolant mass as part of the total, however, this is often missed.
- Cell to Pack designs should have a higher mass ratio
- Structural packs will have a lower mass ratio
There are only a few points here, but it is interesting plotting the mass of the pack minus the cells versus the total pack energy. This shows a scaling of the pack case, busbars, HV system, cooling and mechanics against the size of the pack.
The gradient of the line at 1.59 is 62.9% cell to pack mass ratio.
I need a few more points here and we will gradually add more benchmarks.