Fraction of the theoretical specific energy achieved on pack level for hypothetical battery chemistries

• Fraction of the theoretical specific energy achieved on pack level is estimated.
• Fraction of the theoretical specific energy depends greatly on OCV, Ētheo and ASI.
• Lower Ētheo systems capture higher fraction of the theoretical specific energy.
• Pack-level properties are independent of Ētheo in low OCV systems at moderate ASI.
• Reducing impedance in low OCV systems leads to higher pack-level specific energies.

In valuing new active materials chemistries for advanced batteries, the theoretical specific energy is commonly used to motivate research and development. A packaging factor is then used to relate the theoretical specific energy to the pack-level specific energy. As this factor is typically assumed constant, higher theoretical specific energies are judged to result in higher pack-level specific energies. To test this implicit assumption, we calculated the fraction of the theoretical specific energy achieved on the pack level for hypothetical cell chemistries with various open-circuit voltages and theoretical specific energies using a peer-review bottom-up battery design model. The pack-level specific energy shows significant dependence on the open-circuit voltage and electrochemical impedance due to changes in the quantity of inactive materials required. At low-valued average open-circuit voltages, systems with dramatically different theoretical specific energies may result in battery packs similar in mass and volume. The fraction of the theoretical specific energy achieved on the pack level is higher for the lower theoretical specific energy systems mainly because the active materials mass dominates the pack mass. Finally, low-valued area-specific impedance is shown to be critical for chemistries of high theoretical specific energy and low open-circuit voltage to achieve higher pack-level specific energies.