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 Li 2 Se 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)‐TiO 2 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‐TiO 2 microreactors solidly confining Se actives in spatial regions help to expedite Li 2 Se 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.