Selective S/Li₂S Conversion <i>via</i> in-Built Crystal Facet Self-Mediation: Toward High Volumetric Energy Density Lithium–Sulfur Batteries

TLDR

Gravimetric, areal, and volumetric capacities critically influence secondary battery market penetration, yet carbonaceous cathodes, while boosting gravimetric and areal performance, suffer from poor lithium‑polysulfide fixation, low tap density, and consequently subpar volumetric capacity and cycling stability. The study introduces a sulfur cathode composed of highly conductive ZrB₂ nanoflakes with only 2 wt % conductive carbon. ZrB₂ nanoflakes provide high conductivity and a minimal carbon matrix, enabling efficient electron transport and structural stability. The resulting ZrB₂–S electrode achieves an areal capacity of 8.5 mAh cm⁻², a volumetric energy density of 533 Wh L⁻¹ at a sulfur loading of 7.8 mg cm⁻² with ultralow electrolyte, and spectroscopic/theoretical evidence shows an in‑built Janus crystal facet of exposed B and Zr atoms that selectively mediates lithium‑polysulfide conversion during cycling.

Abstract

The gravimetric, areal, and volumetric capacities pose important influences on market penetration for secondary batteries. Carbonaceous materials take a leading stand for the improvement of gravimetric and areal capacity in lithium–sulfur batteries; however, they exhibit some intrinsic deficiencies, including insufficient fixation on lithium polysulfides (LiPS) and low tap density, incurring poor volumetric performance and inferior cycling behavior. Here, we report a sulfur cathode based on highly conductive ZrB2 nanoflakes with only 2 wt % conductive carbon. The resultant closely packed ZrB2–S electrode delivers a high areal capacity of 8.5 mAh cm–2 and cell-level volumetric energy density of 533 Wh L–1 with a high sulfur loading of 7.8 mg cm–2 and an ultralow electrolyte dosage. With combined spectroscopic studies and theoretical calculation results, it was confirmed that an in-built Janus crystal facet self-mediation is on-site constructed by the exposed B and Zr atoms for an effective bonding and selective conversion on LiPS upon charge–discharge processes.