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

TLDR

Electrochemical energy storage at large scale is a major technological challenge, and researchers are exploring alternative rechargeable battery concepts such as solid‑state, lithium/sulfur, magnesium/sulfur, and dual‑ion batteries that promise high theoretical energies per mass or volume, but theoretical values do not translate directly into practical capacities and voltages, leading to system‑dependent gaps. The study aims to provide high transparency by illustrating which cell components most limit practical energy values and to offer a tool that enables comparison of six battery technologies with clear assumptions. The authors calculate specific energies and energy densities in six successive steps, starting from theoretical active material values and progressing to practical energy values in an 18650 cylindrical cell.

Abstract

Abstract 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.