Pack Gravimetric Energy Density has the units Wh/kg and is a key pack metric. The optimum metric is a high Wh/kg. Hence:
- High nominal voltage
- High Ah capacity
- Low mass
The best you can achieve will be less than or equal to the cell Wh/kg that the pack is made from.
Perhaps the simplest of the battery metrics as the capacity of the cell is fairly easy to measure and the mass is just a set of scales.
The only note of caution is the discharge rate at which the cell Ah capacity has been measured. For automotive C/5 to C/3 is quite representative for a range test. However, for a phone or laptop C/10 is perhaps closer. Most cell capacities are quoted by manufacturers at C/10.
- 171 Wh/kg 2023 Ducati V21L Moto E
- 171 Wh/kg 2021 82kWh Tesla Model 3
- 168 Wh/kg 2019 Renault Zoe ZE 50
- 150 Wh/kg Tesla Model 3 long range version
- 148 Wh/kg 2019 Porsche Taycan Turbo S
- 148 Wh/kg 2018 Jaguar I-Pace
- 147 Wh/kg Formula E Gen 2 Battery Pack 2019-21
- 101 Wh/kg Formula E Gen1 Battery Pack 2014-18
- 80 Wh/kg 2011 Nissan Leaf
- 37.2 Wh/kg Toyota Prius Gen 2 hybrid pack
Plotting this energy density versus total energy in the pack is as expected.
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In aircraft the gravimetric energy density is one of the key targets at pack level. As of 2022 the 400Wh/kg target from NASA is a very tough target when automotive packs are achieving ~170Wh/kg.
NASA state in their November 2021 presentation that they have the following requirements for the battery pack:
- 400 Wh/kg required at the system level
- 1000’s of cycles
- Extremely high power requirements (C-rates) during takeoff and landing
- Cruise power for long range flights
- High reliability, limited maintenance
- Improved safety for thermal runaway events