Flexible SnTe/carbon nanofiber membrane as a free-standing anode for high-performance lithium-ion and sodium-ion batteries

Confining Co1.11Te2 nanoparticles within mesoporous hollow carbon combination sphere for fast and ultralong sodium storage

Co1.11Te2 nanoparticles are in-situ uniformly grown within mesoporous hollow carbon combination sphere (MHCCS@Co1.11Te2) using a hard-template and spray drying process, solution impregnation and pyrolysis tellurization. Material characterizations reveal that Co1.11Te2, with a diameter of ∼ 20 nm, is attached to the internal walls of the unit spheres or embedded in the mesopore shells of the unit spheres, presenting a distinctive "ships-in-combination-bottles" nanoencapsulation structure. In sodium-ion half-cells, MHCCS@Co1.11Te2 exhibits excellent cycling stability, achieving reversible capacities of 257 mAh/g at 0.5 A/g after 250 cycles, 235 mAh/g at 1.0 A/g after 300 cycles and 161 mAh/g at 10.0 A/g after 1900 cycles. Electrochemical kinetic analyses and ex-situ characterizations reveal rapid electron/Na+ transport kinetics, prominent surface pseudocapacitive behavior, robust nanocomposite structure, and multi-step conversion reactions of sodium polytellurides. In sodium-ion full-cells, MHCCS@Co1.11Te2 still demonstrates stable cycling performance at 1.0 and 5.0 A/g and excellent rate capability. The superior electrochemical performance is associated with the nanoencapsulation structure based on mesoporous hollow carbon combination spheres, which promotes electron conduction and Na+ transport. The space-confined effect maintains the high electrochemical activity and cycling stability of Co1.11Te2.

Boosting Manganese Selenide Anode for Superior Sodium-Ion Storage via Triggering α → β Phase Transition

Sodium-ion batteries (SIBs) have been extensively studied owing to the abundance and low-price of Na resources. However, the infeasibility of graphite and silicon electrodes in sodium-ion storage makes it urgent to develop high-performance anode materials. Herein, α-MnSe nanorods derived from δ-MnO2 (δ-α-MnSe) are constructed as anodes for SIBs. It is verified that α-MnSe will be transferred into β-MnSe after the initial Na-ion insertion/extraction, and δ-α-MnSe undergoes typical conversion mechanism using a Mn-ion for charge compensation in the subsequent charge-discharge process. First-principles calculations support that Na-ion migration in defect-free α-MnSe can drive the lattice distortion to phase transition (alpha → beta) in thermodynamics and dynamics. The formed β-MnSe with robust lattice structure and small Na-ion diffusion barrier boosts great structure stability and electrochemical kinetics. Hence, the δ-α-MnSe electrode contributes excellent rate capability and superior cyclic stability with long lifespan over 1000 cycles and low decay rate of 0.0267% per cycle. Na-ion full batteries with a high energy density of 281.2 Wh·kg-1 and outstanding cyclability demonstrate the applicability of δ-α-MnSe anode.

The fabrication of silicon/dual-network carbon nanofibers/carbon nanotubes as free-standing anodes for lithium-ion batteries

Silicon, known for its high theoretical capacity and abundant resources, is regarded as one of the most promising anode materials for lithium-ion batteries (LIBs). However, the application of silicon anode materials is limited by huge expansion and poor electricity of silicon. Herein, a novel free-standing Si/C anode (noted as Si/CNFs/CNTs) is synthesized by combining electrospinning and in situ chemical vapor deposition, in which Si nanoparticles are composited with a conducting dual-network composed of carbon nanofibers (CNFs) and in situ deposited carbon nanotubes (CNTs). In situ deposited CNTs surround the surface of CNFs to form an elastic buffer layer on the surface of Si attached to CNFs, which ensures structural integrity. CNTs with excellent conductivity and a large specific surface area shorten Li+ transport pathways. Therefore, Si/CNFs/CNTs exhibits stable cycling performance and maintains a capacity of 639.9 mA h g-1 and a capacity retention rate of 69.9% after 100 cycles at a current density of 0.1 A g-1. This work provides a promising approach for the structural modification of self-supporting Si/C electrodes.

Sandwich-type N-C@CoTe2@C anode: a stress-buffer nanostructure for stable sodium-ion storage

Transition metal tellurides (TMTes) have received extensive attention for high specific energy sodium-ion batteries (SIBs) due to their high volumetric specific capacity. However, the continuous capacity attenuation arising from the huge volumetric strain during sodiation/desodiation impedes practical applications. Here, we report a "sandwich-type" carbon confinement strategy that entraps cobalt ditelluride (CoTe2) nanocrystals between two carbon layers. Porous cellulose-derived fibres were employed as the inner carbon framework to construct fast conductive circuits and provide an abundant site for anchoring CoTe2 nanocrystals. Polyvinylpyrrolidone (PVP)-derived carbon layers act as carbon armour to encapsulate CoTe2 nanocrystals, inhibiting their volume change and structural pulverization during repeated sodium intercalation/deintercalation. Benefiting from the exquisite structural design, the N-C@CoTe2@C electrode exhibits excellent cycling stability for over 3000 cycles at 2.0 A g-1 and rate performance (113.8 mA h g-1 at 5.0 A g-1). Moreover, ex situ XRD/TEM and kinetic tests revealed a multistep conversion reaction mechanism and a battery-capacitive dual-model Na-storage process. This work provides a new perspective on the development of low-cost and straightforward techniques for fabricating long-life commercial SIB anode materials.

Advanced Anode Materials for Rechargeable Sodium-Ion Batteries

Rechargeable sodium-ion batteries (SIBs) have been considered as promising energy storage devices owing to the similar "rocking chair" working mechanism as lithium-ion batteries and abundant and low-cost sodium resource. However, the large ionic radius of the Na-ion (1.07 Å) brings a key scientific challenge, restricting the development of electrode materials for SIBs, and the infeasibility of graphite and silicon in reversible Na-ion storage further promotes the investigation of advanced anode materials. Currently, the key issues facing anode materials include sluggish electrochemical kinetics and a large volume expansion. Despite these challenges, substantial conceptual and experimental progress has been made in the past. Herein, we present a brief review of the recent development of intercalation, conversion, alloying, conversion-alloying, and organic anode materials for SIBs. Starting from the historical research progress of anode electrodes, the detailed Na-ion storage mechanism is analyzed. Various optimization strategies to improve the electrochemical properties of anodes are summarized, including phase state adjustment, defect introduction, molecular engineering, nanostructure design, composite construction, heterostructure synthesis, and heteroatom doping. Furthermore, the associated merits and drawbacks of each class of material are outlined, and the challenges and possible future directions for high-performance anode materials are discussed.

Ga2Te3-Based Composite Anodes for High-Performance Sodium-Ion Batteries

Recently, metal chalcogenides have received considerable attention as prospective anode materials for sodium-ion batteries (SIBs) because of their high theoretical capacities based on their alloying or conversion reactions. Herein, we demonstrate a gallium(III) telluride (Ga₂Te₃)-based ternary composite (Ga₂Te₃-TiO₂-C) synthesized via a simple high-energy ball mill as a great candidate SIB anode material for the first time. The electrochemical performance, as well as the phase transition mechanism of Ga₂Te₃ during sodiation/desodiation, is investigated. Furthermore, the effect of C content on the performance of Ga₂Te₃-TiO₂-C is studied using various electrochemical analyses. As a result, Ga₂Te₃-TiO₂-C with an optimum carbon content of 10% (Ga₂Te₃-TiO₂-C(10%)) exhibited a specific capacity of 437 mAh·g^-1 after 300 cycles at 100 mA·g^-1 and a high-rate capability (capacity retention of 96% at 10 A·g^-1 relative to 0.1 A·g^-1). The good electrochemical properties of Ga₂Te₃-TiO₂-C(10%) benefited from the presence of the TiO₂-C hybrid buffering matrix, which improved the mechanical integrity and electrical conductivity of the electrode. This research opens a new direction for the improvement of high-performance advanced SIB anodes with a simple synthesis process.

Dual-Type Carbon Confinement Strategy: Improving the Stability of CoTe2 Nanocrystals for Sodium-Ion Batteries with a Long Lifespan

Sodium-ion batteries have great potential to become large-scale energy storage devices due to their abundant and low-cost resources. However, the lack of anode and cathode materials with both high energy density and long-term cycling performance significantly affects their commercial applications. In this work, uniform CoTe₂ nanoparticles are generated from the tellurization of Co nanoparticles, which were coated with polyvinylpyrrolidone in a three-dimensional (3D) porous carbon matrix (CoTe₂@3DPNC). Finally, a dual-type carbon confinement structure is formed after tellurization during which citric acid is adopted as the source of the inner carbon scaffold. The hierarchical carbon matrix not only builds a robust and fast ion/electronic conductive 3D architecture but also mitigates the volume expansion and aggregation of CoTe₂ during sodium insertion/extraction. Remarkably, the CoTe₂@3DPNC electrode displays a high reversible capacity (216.5 mAh g^-1/627.9 mAh cm^-3 at 0.2 A g^-1 after 200 cycles) and outstanding long-term cycling performance (118.1 mAh g^-1/342.5 mAh cm^-3 even at 5.0 A g^-1 after 2500 cycles). Kinetics tests and capacitance calculations clearly reveal a battery-capacitive dual-model Na-storage mechanism. Furthermore, ex situ XRD/SEM/TEM demonstrate superior stability during sodium insertion/extraction. This work provides a valuable strategy for the rational structural design of long-life electrodes for advanced rechargeable batteries.

Three-dimensional flexible molybdenum oxynitride thin film as a high capacity anode for Li-ion batteries

With the fast development of flexible wearable electronics, mobile electronic equipment, electric tool and electric vehicles, high specific capacity, superior cycle stability and excellent fast-charge performance are required for lithium-ion batteries (LIBs). Nevertheless, commercial graphite with the limited theoretical capacity (372 mAh g^-1) and short lifespan is difficult to satisfy the requirements of the new generation of LIBs. In this work, the three-dimensional flexible molybdenum oxynitride (MNO) thin films with non-binder were prepared by magnetron sputtering approach. The charge transfer resistance and Li-ion diffusion coefficient were measured by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the results show that molybdenum nitride is helpful to increase the diffusion and electron transfer of Li-ion. The MNO thin film annealed at 300 °C with irregular aggregate matrix structure shows a discharge capacity of 413 mAh g^-1 after 180 cycles at 1 A g^-1. The outstanding rate performance and cycle stability suggest that these binder-free thin film electrodes, especially nitrides, offer great opportunity for energy storage systems with fast-charge capabilities.