It is a significant challenge to design a dense high-sulfur-loaded cathode and meanwhile to acquire fast sulfur redox kinetics and suppress the heavy shuttling in the lean electrolyte, thus to acquire a high volumetric energy density without sacrificing gravimetric performance for realistic Li–S batteries (LSBs). Herein, we develop a cation-doping strategy to tailor the electronic structure and catalytic activity of MoSe2 that in situ hybridized with conductive Ti3C2T x MXene, thus obtaining a Co-MoSe2/MXene bifunctional catalyst as a high-efficient sulfur host. Combining a smart design of the dense sulfur structure, the as-fabricated highly dense S/Co-MoSe2/MXene monolith cathode (density: 1.88 g cm–3, conductivity: 230 S m–1) achieves a high reversible specific capacity of 1454 mAh g–1 and an ultrahigh volumetric energy density of 3659 Wh L–1 at a routine electrolyte and a high areal capacity of ∼8.0 mAh cm–2 under an extremely lean electrolyte of 3.5 μL mgs –1 at 0.1 C. Experimental and DFT theoretical results uncover that introducing Co element into the MoSe2 plane can form a shorter Co–Se bond, impel the Mo 3d band to approach the Fermi level, and provide strong interactions between polysulfides and Co-MoSe2, thereby enhancing its intrinsic electronic conductivity and catalytic activity for fast redox kinetics and uniform Li2S nucleation in a dense high-sulfur-loaded cathode. This deep work provides a good strategy for constructing high-volumetric-energy-density, high-areal-capacity LSBs with lean electrolytes.

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High-theoretical-capacity silicon anodes hold promise in lithium-ion batteries (LIBs). Nevertheless, their huge volume expansion (∼300%) and poor conductivity show the need for the simultaneous introduction of low-density conductive carbon and nanosized Si to conquer the above issues, yet they result in low volumetric performance. Herein, we develop an integration strategy of a dually encapsulated Si structure and dense structural engineering to fabricate a threedimensional (3D) highly dense Ti 3 C 2 T x MXene and graphene dual-encapsulated Si monolith architecture (HD-Si@Ti 3 C 2 T x @ G). Because of its high density (1.6 g cm −3 ), high conductivity (151 S m −1 ), and 3D dense dual-encapsulated Si architecture, the resultant HD-Si@Ti 3 C 2 T x @G monolith anode displays an ultrahigh volumetric capacity of 5206 mAh cm −3 (gravimetric capacity: 2892 mAh g −1 ) at 0.1 A g −1 and a superior long lifespan of 800 cycles at 1.0 A g −1 . Notably, the thick and dense monolithic anode presents a large areal capacity of 17.9 mAh cm −2 . In-situ TEM and ex-situ SEM techniques, and systematic kinetics and structural stability analysis during cycling demonstrate that such superior volumetric and areal performances stem from its dual-encapsulated Si architecture by the 3D conductive and elastic networks of MXene and graphene, which can provide fast electron and ion transfer, effective volume buffer, and good electrolyte permeability even with a thick electrode, whereas the dense structure results in a large volumetric performance. This work offers a simple and feasible strategy to greatly improve the volumetric and areal capacity of alloy-based anodes for large-scale applications via integrating a dual-encapsulated strategy and dense-structure engineering.

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Fabricating metal boride heterostructures and deciphering their interface interaction mechanism on accelerating polysulfide conversion at atomic levels are meaningful yet challenging in lithium–sulfur batteries (LSBs). Herein, novel highly‐conductive and binary sulfiphilic NbB2‐MXene heterostructures are elaborately designed with spontaneous built‐in electric field (BIEF) via a simple one‐step borothermal reduction strategy. Experimental and theoretical results reveal that Nb and B atoms can chemically bond with polysulfides, thereby enriching chemical anchor and catalytic active sites. Meanwhile, the spontaneous BIEF induces interfacial charge redistribution to make more electrons transferred to surface NbB2 sites, thereby weakening its strong adsorption property yet accelerating polysulfide transfer and electron diffusion on hetero‐interface, so providing moderate polysulfide adsorb‐ability yet decreasing sulfur‐species conversion energy barriers, further boosting the intrinsically catalytic activity of NbB2‐MXene for accelerated bidirectional sulfur conversion. Thus, S/NbB2‐MXene cathode presents high initial capacity of 1310.1 mAh g−1 at 0.1 C, stable long‐term lifespan with 500 cycles (0.076% capacity decay per cycle) at 1 C, and large areal capacity of 6.5 mAh cm−2 (sulfur loading: 7.0 mg cm−2 in lean electrolyte of 5 µL mgs−1) at 0.1 C. This work clearly unveils the mechanism of interfacial BIEF and binary sulfiphilic effect on accelerating stepwise sulfur conversion at atomic levels.