Structure and Interface Engineering of Ultrahigh-Rate 3D Bismuth Anodes for Sodium-Ion Batteries

High-entropy selenides derived from Prussian blue analogues as electrode materials for sodium-ion batteries

Transition metal selenides (TMS) have received much attention as anode materials for sodium-ion batteries (SIBs) because of their high theoretical capacity and excellent redox reversibility. However, their further development is constrained by the dissolution of transition metal ions and substantial volume changes experienced during cycling. Herein, the high-entropy Prussian blue analogues were selenized by the vapor infiltration method, resulting in the formation of a core-shell structured high-entropy selenides (HESe-6). The core-shell structure with voids and abundant selenium vacancies on the surface effectively mitigates bulk expansion and enhances electronic conductivity. Furthermore, the high-entropy property endows an ultra-stable crystal structure and inhibits the dissolution of metal ions. The ex-situ EIS and in-situ XRD results show that HESe-6 is able to be reversibly transformed into highly conductive ultrafine metal particles upon Na+ embedding, providing more Na+ reactive active sites. In addition, despite the incorporation of up to seven different elements, it exhibits minimal phase transitions during discharge/charge cycles, effectively mitigating stress accumulation. HESe-6 could retain an ultralong-term stability of 765.83 mAh g-1 after 1000 loops even at 1 A g-1. Furthermore, when coupled with the Na3V2(PO4)2O2F cathode, it maintains a satisfactory charge energy density of 303 Wh kg-1 after 300 cycles, which shows promising application prospect in the future.

Interfacial SbOC bond and structural confinement synergistically boosting the reaction kinetics and reversibility of Sb2Se3/NC nanorods anode for sodium storage

Antimony selenide (Sb2Se3) has been considered as a prospective material for sodium-ion batteries (SIBs) because of its large theoretical capacity. Whereas, grievous volume expansion caused by the conversion-alloying reaction leads to fast capacity decay and inferior cycle stability. Herein, the confined Sb2Se3 nanorods in nitrogen-doped carbon (Sb2Se3/NC) with interfacial chemical bond is designed to further enhance sodium storage properties of Sb2Se3. The robust enhancing effect of interfacial SbOC bonds can significantly promote electron transfer, Na+ ions diffusion kinetics and alloying reaction reversibility, combining the synergistic effect of the unique confinement structure of N-doped carbon shells can efficiently alleviate the volume change to ensure the structural integrity. Moreover, in-situ X-ray diffraction reveals intercalation/de-intercalation, conversion/reversed conversion reaction and alloying/de-alloying reaction mechanisms, and the kinetics analysis demonstrates the diffusion-controlled to contribute high capacity. As a result, Sb2Se3/NC anode delivers a high reversible capacity of 612.6 mAh/g at 0.1 A/g with a retentive specific capacity of 471.4 mAh/g after 1000 cycles, and long-cycle durability of over 2000 cycle with the reversible capacities of 371.1 and 297.3 mAh/g at 1 and 2 A/g are achieved, respectively, and an good rate capability. This distinctive interfacial chemical bonds and confinement effect design shows potential applications in the improved conversion/alloying-type materials for SIBs.

Facilitating Rapid Na+ Storage through MoWSe/C Heterostructure Construction and Synergistic Electrolyte Matching Strategy

The realization of sodium-ion devices with high-power density and long-cycle capability is challenging due to the difficulties of carrier diffusion and electrode fragmentation in transition metal selenide anodes. Herein, a Mo/W-based metal-organic framework is constructed by a one-step method through rational selection, after which MoWSe/C heterostructures with large angles are synthesized by a facile selenization/carbonization strategy. Through physical characterization and theoretical calculations, the synthesized MoWSe/C electrode delivers obvious structural advantages and excellent electrochemical performance in an ethylene glycol dimethyl ether electrolyte. Furthermore, the electrochemical vehicle mechanism of ions in the electrolyte is systematically revealed through comparative analyses. Resultantly, ether-based electrolytes advantageously construct stable solid electrolyte interfaces and avoid electrolyte decomposition. Based on the above benefits, the Na half-cell assembled with MoWSe/C electrodes demonstrated excellent rate capability and a high specific capacity of 347.3 mA h g-1 even after cycling 2000 cycles at 10 A g-1. Meanwhile, the constructed sodium-ion capacitor maintains ∼80% capacity retention after 11,000 ultralong cycles at a high-power density of 3800 W kg-1. The findings can broaden the mechanistic understanding of conversion anodes in different electrolytes and provide a reference for the structural design of anodes with high capacity, fast kinetics, and long-cycle stability.

Well-Dispersed Bi nanoparticles for promoting the lithium storage performance of Si Anode: Effect of the bridging Bi nanoparticles

Silicon (Si) is considered a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity of up to 4200 mAh/g. However, the poor cycling and rate performances of Si induced by the low intrinsic electronic conductivity and large volume expansion during the lithiation/delithiation process limit its practical application. Herein, a novel silicon/bismuth@nitrogen-doped carbon (Si/Bi@NC) composite with nanovoids was synthesized and investigated as an advanced anode material for LIBs. In such a structure, ultrafine bismuth nanoparticles coupled with an N-doped carbon layer were introduced to modify the surface of Si nanoparticles. Subsequently, the lithiated LixBi has excellent high ionic conductivity and acts as a fast transport bridge for lithium ions. The introduced carbon coating layer and nanovoids can buffer the volume expansion of Si during the lithiation/delithiation process, thus maintaining structural stability during the cycling process. As a result, the Si/Bi@NC composite exhibits excellent electrochemical performance, providing a relatively high capacity of 955.8 mAh/g at 0.5 A/g after 450 cycles and excellent rate performance with a high capacity of 477.8 mAh/g even at 10.0 A/g. Furthermore, the assembled full cell with LiFePO4 as cathode and pre-lithium Si/Bi@NC as anode can provide a high capacity of 138.8 mAh/g at 1C after 90 cycles, exhibiting outstanding cycling performance.

Highly Stable ZnS Anodes for Sodium-Ion Batteries Enabled by Structure and Electrolyte Engineering

Zinc sulfide is a promising high-capacity anode for practical sodium-ion batteries, considering its high capacity and the low cost of zinc and sulfur sources. However, the pulverization of particulate zinc sulfide causes active mass collapse and penetration-induced short circuits of batteries. Herein, a zinc sulfide encapsulated in a nitrogen-doped carbon shell (ZnS@NC) was developed for high-performance anodes. The confinement effect of nitrogen-doped carbon stabilizes the active mass structure during cycling thanks to the robust chemically and electronically bonded connections between nitrogen-doped carbon and zinc sulfide nanoparticles. Furthermore, the cycling stability of the ZnS@NC anode is boosted by the robust inorganic-rich solid electrolyte interphase (SEI) formed in cyclic and linear ether-based electrolytes. The ZnS@NC anode displayed a reversible specific capacity of 584 mAh g-1, an excellent rate capability of 327 mAh g-1 at 70 A g-1, and a highly stable cycling performance over 10000 cycles. This work provides a practical and promising approach to designing stable conversion anodes for high-performance sodium-ion batteries.

Bismuth-Antimony Alloy Nanoparticles Embedded in 3D Hierarchical Porous Carbon Skeleton Film for Superior Sodium Storage

A composite film that features bismuth-antimony alloy nanoparticles uniformly embedded in a 3D hierarchical porous carbon skeleton is synthesized by the polyacrylonitrile-spreading method. The dissolved polystyrene is used as a soft template. The average diameter of the bismuth-antimony alloy nanoparticles is ~34.5 nm. The content of the Bi-Sb alloy has an impact on the electrochemical performance of the composite film. When the content of the bismuth-antimony alloy is 45.27%, the reversible capacity and cycling stability of the composite film are the best. Importantly, the composite film outperforms the bismuth-antimony alloy nanoparticles embedded in dense carbon film and the cube carbon nanobox in terms of specific capacity, cycling stability, and rate capability. The composite film can provide a discharge capacity of 322 mAh g-1 after 500 cycles at 0.5 A g-1, 292 mAh g-1 after 500 cycles at 1 A g-1, and 185 mAh g-1 after 2000 cycles at 10 A g-1. The carbon film prepared by the spreading method presents a unique integrated composite structure that significantly improves the structural stability and electronic conductivity of Bi-Sb alloy nanoparticles. The 3D hierarchical porous carbon skeleton structure further enhances electrolyte accessibility, promotes Na+ transport, increases reaction kinetics, and buffers internal stress.