Theoretical versus Practical Energy: A Plea for More Transparency in the Energy Calculation of Different Rechargeable Battery Systems

Electrochemical energy storage at a large scale poses one of the main technological challenges of this century. The scientific community in academia and industry worldwide intensively is exploring various alternative rechargeable battery concepts beside state-of-the-art lithium ion batteries (LIBs), for example, all-solid-state batteries, lithium/sulfur batteries, magnesium/sulfur batteries or dual-ion batteries that could outperform LIBs in different aspects. Often, these concepts also promise very high theoretical energies per mass or volume. However, as theoretical values exclude numerous relevant parameters, they do not translate directly into practically achievable energy values: The gaps between practical capacities and voltages compared to the theoretical values differ for each system. In order to provide high transparency and to illustrate which cell components are most important in the limitation of the practical energy values, in this study, the specific energies and energy densities are calculated in six subsequent steps-from the theoretical energy values of the active materials alone to the practical energy values in an 18650 cylindrical cell. By providing a tool to calculate the energy values of six different battery technologies with different assumptions made evident, this study aims for more transparency and reliability in the comparison of different cell chemistries.