Thermodynamic analysis on energy densities of batteries

TLDR

Secondary battery energy density has risen at an average rate of about 3 % per year over the past 60 years. The paper evaluates energy densities of Li‑ion and other metal‑based batteries, examines storage capacities and conversion reactions, and seeks breakthroughs to raise Li‑ion energy density from 210 Wh kg⁻¹ to the 500–700 Wh kg⁻¹ target for electric vehicles. Thermodynamic calculations of theoretical energy densities for 1,172 systems were performed to identify practical limits and screen promising chemistries. The Li/F₂ system achieves the highest theoretical energy density, with Li/O₂ second, both roughly ten times higher than current Li‑ion batteries.

Abstract

The average increase in the rate of the energy density of secondary batteries has been about 3% in the past 60 years. Obviously, a great breakthrough is needed in order to increase the energy density from the current 210 Wh kg−1 of Li-ion batteries to the ambitious target of 500–700 Wh kg−1 to satisfy application in electrical vehicles. A thermodynamic calculation on the theoretical energy densities of 1172 systems is performed and energy storage mechanisms are discussed, aiming to determine the theoretical and practical limits of storing chemical energy and to screen possible systems. Among all calculated systems, the Li/F2 battery processes the highest energy density and the Li/O2 battery ranks as the second highest, theoretically about ten times higher than current Li-ion batteries. In this paper, energy densities of Li-ion batteries and a comparison of Li, Na, Mg, Al, Zn-based batteries, Li-storage capacities of the electrode materials and conversion reactions for energy storage, in addition to resource and environmental concerns, are analyzed.