Elevated Practical Volumetric Density and Cyclic Durability of Selenium Cathodes by Powder Microspheroidization and Kilogram-Scale Atomic Layer Deposition Techniques

Abstract

Practical usage of high-energy chalcogen cathodes, typically like selenium (Se), is plagued by compromised volumetric energy density and cyclic lifespan in pouch cells, due to the low cathode compactness and continuous Li₂Se_n shutting issues. Inspired by classic close-packing theories and self-limiting configurations, we propose to construct high-tap-density microsphere cathodes made of Se nano yolks and N-rich carbon (NC)-TiO₂ shells via a kilogram-scale atomic layer deposition (ALD) technique. The utilized particle microspheroidization strategy makes powders approach the Max. theoretical volume fraction of 0.64, achieving intrinsically high tap density (2.06 g cm⁻³) and large areal Se loading ratio beyond 8.4 mg cm⁻² after slurry coating. A molecular-engineered oxidative polypyrrole (O-PPy) layer covered on Se surfaces plays an indispensable role in guaranteeing smooth ALD implementation. The formed robust NC-TiO₂ microreactors solidly confining Se actives in spatial regions help to expedite Li₂Se_n phase conversions, rendering cathodes with a remarkable capacity of 502 mAh g⁻¹ (0.5C) and far lessened capacity decay in all cycling. Their assembled pouch cells are ∼20% thinner than those of random-shaped counterparts, showing an exceptionally high E_v value over 1158.3 Wh L⁻¹. This work may propel the advent of Li-chalcogen cells with unprecedented volumetric energy densities for near-future applications.