Characteristic analysis of lithium–oxygen batteries considering the discontinuous deposit and electrolyte degradation effects during discharge

Abstract

The modeling research plays a crucial role in grasping the reaction mechanisms and forecasting the performance of lithium‑oxygen (LiO2) batteries. A transient LiO2 battery model including continuity, transportation, and reaction kinetics by simultaneously considering the discontinuous deposit of discharge product Li2O2 and the formation of by-product Li2CO3 due to electrolyte degradation, is developed to reveal the discharge phenomena. The effects of operating conditions and electrolyte and electrode properties on the discharge behaviors including voltage-capacity curve, energy density, profiles of O2 concentration (CO2) and porosity (ɛ) at the cathode are quantitatively studied. It is found that enhancing O2 solubility (SO2) and diffusivity (DO2) significantly improves discharge capacity and voltage plateau; the promotion of voltage plateau will be inconspicuous as electrolyte conductivity (κ) is enlarged over 1 S/m. With the rise of ɛ from 0.73 to 0.93, the specific capacity is boosted from 874 to 6122 mAh/g‑carbon, and the corresponding specific energy upgrades from 2260 to 15,610 mWh/g‑carbon. Shortening cathode thickness (Lca) facilitates the efficient utilization of carbon cathode material but this comes at the expense of lowering the mass loading of carbon, the practical energy drops 59.4 % as Lca reduces from 750 μm to 100 μm. After 20 consecutive charge-discharge cycles, the capacity retention obtained is 36.884 %, accompanied by a 13.8 % volume fraction of Li2CO3 formation inside the cathode. This work may guide in designing electrodes and electrolytes and provide performance regulation strategies for LiO2 batteries.