Xiaoyu Cao

Investigation of the Sodium Ion Pathway and Cathode Behavior in Na3V2(PO4)2F3 Combined via a First Principles Calculation

The electrochemical properties of Na3V2(PO4)2F3 cathode utilized in the sodium ion battery are investigated, and the ion migration mechanisms are proposed as combined via the first principles calculations. Two different Na sites, namely, the Na(1) and Na(2) sites, could cause two sodium ions of Na3V2(PO4)2F3 to be extracted or inserted by a two-step electrochemical process accompanied by structural reorganization that could be responsible for the redox reaction of V(3+/4+). Because the calculated average voltage (V(avg)) of the second charging plateau is 4.04 V for the optimized system but 4.38 V for the unoptimized one, the reorganization of the cathode system can make a stable configuration and lower the extraction energy. Three designed pathways for sodium ions along the x, y, z directions in Na3V2(PO4)2F3, known as a 3D ions transport tunnel, have activation energies (Ea) of 0.449, 0.2, and 0.323 eV, respectively, by using DFT calculations, demonstrating the different feasibilities of the migration directions.

Rodlike Sb2Se3 Wrapped with Carbon: The Exploring of Electrochemical Properties in Sodium-Ion Batteries

One-dimensional Sb2Se3/C rods are prepared through self-assembly by inducing anisotropy, and their corresponding sodium storage behaviors are evaluated, presenting excellent electrochemical performances with superior cycling stability and rate capability. Sb2Se3 delivers a high initial charge capacity of 657.6 mA h g-1 at a current density of 0.2 A g-1 between 2.5 and 0.01 V. After 100 cycles, the reversible capacity of Sb2Se3/C is still retained at 485.2 mA h g-1. Even at a high rate current density of 2.0 A g-1, the charge capacity is still retained at 311.5 mA h g-1. Through the analysis of cyclic voltammetry and in situ electrochemical impedance spectroscopy, the in-depth understanding of high rate performances is explored effectively. Briefly, the sodium storage performance of Sb2Se3/C is observably enhanced, benefiting from the 1D structure and the introduction of a carbon layer with robust structure stability and conductivity.

Multidimensional Evolution of Carbon Structures Underpinned by Temperature‐Induced Intermediate of Chloride for Sodium‐Ion Batteries

Abstract Different dimensions of carbon materials with various features have captured numerous interests due to their applications on the tremendous fields. Restricted by the raw materials and devices, the controlling of their morphology is a major challenge. Utilizing the catalytic features of the intermediates from the low‐cost salts and polymerization of 0D carbon quantum dots (CQDs), 0D CQDs are expected to self‐assemble into 1/2/3D carbon structures with the assistance of temperature‐induced intermediates (e.g., ZnO, Ni, and Cu) from the salts (ZnCl2, NiCl2, and CuCl). The formation mechanisms are illustrated as follows: 1) the “orient induction” to evoke “vine style” growth mechanism of ZnO; 2) the “dissolution–precipitation” of Ni; and 3) the “surface adsorption self‐limited” of Cu. Subsequently, the degree of graphitization, interlayer distance, and special surface area are investigated in detail. 1D structure from 700 °C as anode displays a high Na‐storage capacity of 301.2 mAh g−1 at 0.1 A g−1 after 200 cycles and 107 mAh g−1 at 5.0 A g−1 after 5000 cycles. Quantitative kinetics analysis confirms the fundamentals of the enhanced rate capacity and the potential region of Na‐insertion/extraction. This elaborate work opens up an avenue toward the design of carbon with multidimensions and in‐depth understanding of their sodium‐storage features.

Sulfur-doped carbon employing biomass-activated carbon as a carrier with enhanced sodium storage behavior

Restricted by their high specific surface area and porous structures, activated carbon (AC) materials display poor performances, such as a low initial coulombic efficiency in sodium-ion batteries (SIBs). Nevertheless, it is an ideal choice for carriers, where the high specific surface area is indispensable. Herein, a novel strategy to design S-doped carbon employing durian shell-based AC (DSAC) as the template is proposed and the effect of the amount of DSAC additive was investigated in detail. Impressively, an optimized amount of DSAC additive would contribute to the good dispersion of poly-2-thiophenemethanol (sulfur source) as well as an increased number of active sites for Na storage, thus resulting in excellent electrochemical performance. A high reversible specific capacity of 345 mA h g−1 was attained and the specific capacity of 264 mA h g−1 was retained after 200 cycles. In particular, a high initial coulombic efficiency of 56.02% and remarkable rate capability of 100.02 mA h g−1 were achieved at 5 A g−1 even after 4500 cycles. Meaningfully, the proposed route used to prepare carbon materials for SIBs can effectively facilitate the further application of AC and the construction of high-performance electrode materials for SIBs.

3D hollow porous carbon microspheres derived from Mn-MOFs and their electrochemical behavior for sodium storage

Extensive efforts have been put into developing new materials with a 3D hollow porous spherical structure for increasing their applications in energy storage. In this work, 3D hollow porous carbon microspheres (3DHPCMs) are firstly prepared by the carbonization and post acid-treatment of 3D hollow microspherical Mn-MOFs (3DMn-MOFs), showing a high surface area of 788.2 m2 g−1 and a diameter of about 2 μm. Importantly, this is the first time that the conversion from 1D nanorods to 3D hollow spheres of Mn-MOFs through regulating the amount of poly(vinylpyrrolidone) (PVP) has been realized. Besides, the sodium storage behavior of 3D hollow porous carbon microspheres is also firstly studied. When utilized as anodes for sodium ion batteries (SIBs), the 3DHPCMs deliver excellent electrochemical storage performances with a high specific capacity of 313.8 mA h g−1 at a current density of 100 mA g−1. Impressively, a high discharge specific capacity of 112.5 mA h g−1 is obtained at 5 A g−1. The outstanding electrochemical performances can be attributed to the 3D hollow porous microsphere structure, which can enhance the mechanical stability, buffer the volume expansion, and accelerate the transport of Na+ and electrons. This work provides a new route for the development of materials with a 3D hollow spherical structure.

LiV3O8/Polydiphenylamine Composites with Significantly Improved Electrochemical Behavior as Cathode Materials for Rechargeable Lithium Batteries

Although LiV3O8 is regarded as a potential cathode candidate for rechargeable lithium batteries, it has been restricted by its weak dissolution and lattice structure change. Here, polydiphenylamine is successfully introduced to trigger the evolution of LiV3O8 material through an in situ oxidative polymerization method, significantly improving the electrochemical properties and inhibiting the adverse reaction. Expectedly, the 10 wt % LiV3O8/polydiphenylamine composite delivers a high initial specific discharge capacity of 311 mAh g-1, which decreases to 272 mAh g-1 after 50 cycles at the current density of 60 mA g-1. Even at a high current density of 2000 mA g-1, it still exhibited a reversible specific capacity of 125 mAh g-1 after 50 cycles. Quantitative kinetics analysis confirms the fundamental reasons for the enhanced rate capability. The ex situ X-ray diffraction and scanning electron microscopy results suggest that 10 wt % LiV3O8/polydiphenylamine composite possesses an ultrahigh structural stability during cycling.

Hollow-sphere ZnSe wrapped around carbon particles as a cycle-stable and high-rate anode material for reversible Li-ion batteries

Hollow-sphere ZnSe is successfully obtained through Ostwald ripening. Carbon nanoparticles are designed and utilized to form a wrapped carbon network as a conductive buffering matrix by subsequent annealing. The ZnSe/C composites, as anode materials for lithium-ion batteries (LIBs), exhibit excellent Li+ storage properties, delivering a high reversible capacity of 573.7 mA h g−1 at 1.0 A g−1 after 800 cycles. Even upon increasing the high current density to 20.0 A g−1, the reversible capacity can achieve 318.8 mA h g−1 after 5000 cycles. The superior rate capability is confirmed through the current density return from 20.0 to 1.0 A g−1, and ZnSe/C composites still recover up to 469 mA h g−1, with a retention of 92%. The enhanced electrochemical performances of ZnSe/C composites are attributed to the unique structure and the introduction of conductive carbon networks, which can improve the Li+ diffusion coefficient in the insertion and extraction process. Furthermore, the interconnected network also alleviates the volume variation during cycling and further enhances the structural stability.