Enhanced Structural Stability and Volumetric Capacity of a 3D Pyknotic Graphene Conductive Network via a Pillar Effect of Sn Nanoparticles for Sodium-Ion Batteries

Facile and Scalable Development of High-Performance Carbon-Free Tin-Based Anodes for Sodium-Ion Batteries

Tin (Sn)-based anodes for sodium (Na)-ion batteries possess higher Na-storage capacity and better safety aspects compared to hard carbon -based anodes but suffer from poor cyclic stability due to volume expansion/contraction and concomitant loss in mechanical integrity during sodiation/desodiation. To address this, the usage of nanoscaled electrode-active particles and nanoscaled-carbon-based buffers has been explored, but with compromises with the tap density, accrued irreversible surface reactions, overall capacity (for "inactive" carbon), and adoption of non-scalable/complex preparation routes. Against this backdrop, anode-active "layered" bismuth (Bi) has been incorporated with Sn via a facile-cum-scalable mechanical-milling approach, leading to individual electrode-active particles being composed of well-dispersed Sn and Bi phases. The optimized carbon-free Sn-Bi compositions, benefiting from the combined effects of "buffering" action and faster Na transport of Bi, to go with the greater Na-storage capacity and lower operating potential of Sn, exhibit excellent cyclic stability (viz., ∼83-92% capacity retention after 200 cycles at 1C) and rate capability (viz., no capacity drop from C/5 to 2C, with only ∼25% drop at 5C), despite having fairly coarse particles (∼5-10 μm). As proven by operando synchrotron X-ray diffraction and stress measurements, the sequential sodiation/desodiation of the components and, concomitantly, stress build-ups at different potentials provide "buffering" action even for such "active-active" Sn-Bi compositions. Furthermore, the overall stress development upon sodiation of Bi has been found to be significantly lower than that of Sn (by a factor of ∼3.8), which renders Bi promising as a "buffer" material, in general. Dissemination of such complex interplay between electrode-active components during electrochemical cycling also paves the way for the development of high-performance, safe, and scalable "alloying-reaction"-based anode materials for Na-ion batteries and beyond, sans the need for ultrafine/nanoscaled electrode particles or "inactive" nanoscaled-carbon-based "buffer" materials.

High-Capacity Sb/Fe2S3 Sodium-Ion Battery Anodes Fabricated by a One-Step Redox Reaction, Followed by Ball Milling with Graphite

Antimony (Sb) has been considered a promising anode for sodium-ion batteries (SIBs) owing to its high theoretical capacity (660 mA h g^-1) and low redox voltage (0.2-0.9 V vs Na⁺/Na). However, the capacity degradation caused by the volumetric variation during battery discharge/charge hinders the practical application. Herein, guided by the DFT calculation, Sb/Fe₂S₃ was fabricated by annealing Fe and Sb₂S₃ mixed powder. Next, Sb/Fe₂S₃ was blended with 15 wt % graphite by ball milling, yielding nano-Sb/Fe₂S₃ anchored on an exfoliated graphite composite (denoted as Sb/Fe₂S₃-15%). When applied as an anode of SIBs, Sb/Fe₂S₃-15% delivered reversible capacities of 565, 542, 467, 366, 285, and 236 mA h g^-1 at current rates of 1, 2, 4, 6, 8, and 10 A g^-1, respectively, surpassing most of the Sb-based anodes. The co-existence of highly conductive Fe₂S₃ and Sb minimizes the polarization of the anode. Our experiments proved that the Sb and Fe₂S₃ phases were reversible during discharge/charge cycling, and the exfoliated graphite can accelerate the Na⁺ diffusion and e^- conduction. The proposed synthesis method of this work can also be applicable to synthesize various antimony/transition metal sulfide heterostructures (Sb/M_1-xS), which may be applied in a series of fields.

Bowl-shaped hollow carbon wrapped in graphene grown in situ by chemical vapor deposition as an advanced anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) are expected to be ideal alternatives to lithium-ion batteries (LIBs) in the future due to their abundant and low-cost resource advantages. A key challenge in SIBs is the development of anodes capable of insertion/extraction of sodium ions (Na⁺) with large radii. Here, hollow bowl-shaped porous carbon materials are uniformly modified with vertically grown graphene (denoted as HBC/VGSs) demonstrating a large specific surface area and three-dimensional structure, which are employed as a viable high-performance anode for SIBs. HBC/VGSs anodes are highly effective at storing sodium because of their structural features. As a result, the HBC/VGSs electrodes provide a high reversible capacity of 409 mAh g^-1 after 100 cycles at 0.1 A g^-1, as well as outstanding rate capability (301.6 mAh g^-1 at 5 A g^-1). Moreover, it also shows extraordinary cycling stability (230.3 mAh g^-1 after 2500 cycles at a high current density of 5 A g^-1) that is significantly better than the pristine hollow bowl-shaped porous carbon (HBC). Cyclic Voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT) were used to analyze the pseudocapacitance and sodium storage kinetics. It was found that high electrical conductivity and large surface area can improve Na⁺ adsorption and diffusion, enhance the electronic conductivity, and deliver superior capacity and rate. The results, taken as a whole, provide new insight into the creation of long-lasting carbon anodes that deliver optimal performance in SIBs.