Diffusional Features of a Lithium-Sulfur Battery Exploiting Highly Microporous Activated Carbon

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• The performance of lithium-sulfur (Li-S) batteries is significantly influenced by diffusion processes at the electrode/electrolyte interphase.
• Activated carbon (AC) plays a crucial role in facilitating ion and polysulfide transport within this interphase region.

Purpose of the Study:

• To investigate the diffusion coefficients of lithium ions (Li+) in Li-S batteries utilizing highly porous activated carbon.
• To explore the dependence of these diffusion coefficients on the battery's state of charge and the measurement techniques employed.
• To correlate diffusion trends with the underlying reaction mechanisms in Li-S batteries.

Main Methods:

• Characterization of heteroatoms (N, S, O, P) in bioresidue-derived AC using X-ray photoelectron spectroscopy (XPS) and X-ray energy dispersive spectroscopy (EDS).
• Measurement of transport properties via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT).

Main Results:

• The Li+ diffusion coefficient (DLi+) values were found to be technique-dependent, ranging from 10⁻⁷–10⁻⁸ cm²/s (EIS), 10⁻⁸–10⁻⁹ cm²/s (CV), and 10⁻⁶–10⁻¹² cm²/s (GITT).
• DLi+ generally decreases at the fully discharged state and increases upon charging, with GITT revealing the formation of low-conducting media during discharge.
• The sulfur composite electrodes demonstrated specific capacities from 1300 mAh/g (0.1C) to 700 mAh/g (2C) at 2 mg/cm² S loading, and 1000–800 mAh/g at 0.2C with 6 mg/cm² S loading.

Conclusions:

• The study highlights the critical role of activated carbon in enhancing ion transport in Li-S batteries.
• Understanding the technique-dependent diffusion behavior and its correlation with the state of charge is essential for optimizing Li-S battery design.
• The characterized heteroatom-doped AC shows promise for improving the electrochemical performance of Li-S batteries.