Investigation of the effect of load weight on the discharge capacity of lithium–o2 batteries using carbon-paper–based electrodes

Abstract

We prepared carbon electrodes with nearly uniform thickness and varying loading weights using carbon paper (CP) as a support material and current collector for single-walled carbon nanotubes (SWCNTs). These electrodes were used as the positive electrode in a lithium–O2 battery, tested at a lower voltage limit of 2.4 V with a fixed current of 0.26 mA/cm2 (0.5 mA). Results demonstrated that the discharge gravimetric capacity (capacity normalized per weight of SWCNTs) did not change significantly for loading weights ≥0.42 mg/cm2. However, for loading weights <0.42 mg/cm2, the discharge gravimetric capacity exhibited an inverse correlation with weight. Analysis of the prepared electrodes revealed that at very low SWCNT loading weights, the sheets of SWCNTs became extremely thin, leading to occasional tears. Nonetheless, these structural changes had no significant impact on the specific surface area or contact resistance. Further analysis of the post-test electrodes using scanning electron microscopy and X-ray diffraction, along with considerations of the carbon paper's surface area as a percentage of the total electrode surface, led to the conclusion that at low loading weights, CP actively contributes to the discharge process and serves as a deposition site for Li2O2. Consequently, when the weight of the active material falls below a certain threshold, there is a risk of misperception, potentially leading to an overestimation of the discharge capacity.