A core–shell electrode for dynamically and statically stable Li–S battery chemistry

Abstract

Sulfur is an appealing cathode material for establishing advanced lithium batteries as it offers a high theoretical capacity of 1675 mA h g⁻¹ at low material and operating costs. However, the lithium–sulfur (Li–S) electrochemical cells face several formidable challenges arising from both the materials chemistry (e.g., low electrochemical utilization of sulfur and severe polysulfide diffusion) and battery chemistry (e.g., dynamic and static instability and low sulfur loadings). Here, we present the design of a core–shell cathode with a pure sulfur core shielded within a conductive shell-shaped electrode. The new electrode configuration allows Li–S cells to load with a high amount of sulfur (sulfur loadings of up to 30 mg cm⁻² and sulfur content approaching 70 wt%). The core–shell cathodes demonstrate a superior dynamic and static electrochemical stability in Li–S cells. The high-loading cathodes exhibit (i) a high sulfur utilization of up to 97% at C/20–C/2 rates and (ii) a low self-discharge during long-term cell storage for a three-month rest period and at different cell-storage conditions. Finally, a polysulfide-trap cell configuration is designed to evidence the eliminations of polysulfide diffusion and to investigate the relationship between the electrode configuration and electrochemical characteristics. The comprehensive analytical results based on the high-loading cathodes suggest that (i) the core–shell cathode is a promising solution for designing highly reversible Li–S cells and (ii) the polysulfide-trap cell configuration is a viable approach to qualitatively evaluating the presence or absence of polysulfide diffusion.