Green and Scalable Template-Free Strategy to Fabricate Honeycomb-Like Interconnected Porous Micro-Sized Layered Sb for High-Performance Potassium Storage.

The tremendous volume change and severe pulverization of micro-sized Sb anode generate no stable capacity in potassium-ion batteries (PIBs). The honeycomb-like porous structure provides free spaces to accommodate its volume expansion and offers efficient ion transport, yet complex synthesis and low yield limits its large-scale application. Here, a green, scalable template-free method for designing a 3D honeycomb-like interconnected porous micro-sized Sb (porous-Sb) is proposed. Its honeycomb-like porous formation mechanism is also verified. Under hydrothermal conditions, Sb reacts with water and dissolved oxygen in water, undergoing non-homogeneous and continuous corrosion at grain boundaries, and producing soluble H2 Sb2 O6 (H2 O), which regulates the porous structure of Sb by controlling reaction time. Benefiting from its porous structure and micron size, porous-Sb anode displays large gravimetric and volumetric capacities with 655.5 mAh g-1 and 2,001.9 mAh cm-3 at 0.05 A g-1 and superior rate performance of 441.9 mAh g-1 at 2.0 A g-1 in PIBs. Furthermore, ex situ characterization and kinetic analysis uncover the small volume expansion and fast K+ reaction kinetics of porous Sb during potassiation/depotassiation, originating from its large electrolyte contact area and internal expansion mechanism. It verifies a green, scalable template-free strategy to construct honeycomb-like porous metals for energy storage and conversion.

Integrating Dually Encapsulated Si Architecture and Dense Structural Engineering for Ultrahigh Volumetric and Areal Capacity of Lithium Storage.

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 three-dimensional (3D) highly dense Ti3C2Tx MXene and graphene dual-encapsulated Si monolith architecture (HD-Si@Ti3C2Tx@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@Ti3C2Tx@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.

Ultrahigh-Volumetric-Energy-Density Lithium-Sulfur Batteries with Lean Electrolyte Enabled by Cobalt-Doped MoSe2/Ti3C2Tx MXene Bifunctional Catalyst.

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 Ti3C2Tx 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.

Green, Template-Less Synthesis of Honeycomb-like Porous Micron-Sized Red Phosphorus for High-Performance Lithium Storage.

Large-volume-expansion-induced material pulverization severely limits the electrochemical performance of high-capacity red phosphorus (RP) in alkali-ion batteries. Honeycomb-like porous materials can effectively solve the issues due to their abundant interconnected pore structures. Nevertheless, it is difficult and greatly challenging to fabricate a honeycomb-like porous RP that has not yet been fabricated via chemical synthesis. Herein, we successfully fabricate a honeycomb-like porous micron-sized red phosphorus (HPRP) with a controlled pore structure via a large-scale green and template-less hydrothermal strategy. It is demonstrated that dissolved oxygen in the solution can accelerate the destruction of P9 cages of RP, thus forming abundant active defects with a faster reaction rate, so the fast corrosion forms the honeycomb-like porous structure. Owing to the free volume, interconnected porous structure, and strong robustness, the optimized HPRP-36 can mitigate drastic volume variation and prevent pulverization during cycling resulting in tiny particle-level outward expansion, demonstrated by in situ TEM and ex situ SEM analysis. Thus, the HPRP-36 anode delivers a large reversible capacity (2587.4 mAh g-1 at 0.05 A g-1) and long-cycling stability with over 500 cycles (∼81.9% capacity retention at 0.5 A g-1) in lithium-ion batteries. This generally scalable, green strategy and deep insights provide a good entry point in designing honeycomb-like porous micron-sized materials for high-performance electrochemical energy storage and conversion.

Ultrahigh and Durable Volumetric Lithium/Sodium Storage Enabled by a Highly Dense Graphene-Encapsulated Nitrogen-Doped Carbon@Sn Compact Monolith.

Tin-based composites hold promise as anodes for high-capacity lithium/sodium-ion batteries (LIBs/SIBs); however, it is necessary to use carbon coated nanosized tin to solve the issues related to large volume changes during electrochemical cycling, thus leading to the low volumetric capacity for tin-based composites due to their low packing density. Herein, we design a highly dense graphene-encapsulated nitrogen-doped carbon@Sn (HD N-C@Sn/G) compact monolith with Sn nanoparticles double-encapsulated by N-C and graphene, which exhibits a high density of 2.6 g cm-3 and a high conductivity of 212 S m-1. The as-obtained HD N-C@Sn/G monolith anode exhibits ultrahigh and durable volumetric lithium/sodium storage. Specifically, it delivers a high volumetric capacity of 2692 mAh cm-3 after 100 cycles at 0.1 A g-1 and an ultralong cycling stability exceeding 1500 cycles at 1.0 A g-1 with only 0.019% capacity decay per cycle in lithium-ion batteries. Besides, in situ TEM and ex situ SEM have revealed that the unique double-encapsulated structure effectively mitigates drastic volume variation of the tin nanoparticles during electrode cycling. Furthermore, the full cell using HD N-C@Sn/G as an anode and LiCoO2 as a cathode displays a superior cycling stability. This work provides a new avenue and deep insight into the design of high-volumetric-capacity alloy-based anodes with ultralong cycle life.