Strain Redistribution in Metal‐Sulfide‐Composite Anode for Enhancing Volumetric Lithium Storage

High performance of membrane capacitive deionization with ZnS/g-C3N4 composite electrodes

Capacitive deionization (CDI) is considered a promising technology for desalination of sea or brackish water. In this study, a ZnS/g-C3N4 composite was synthesized through a one-step high-temperature method and used as the main material to fabricate CDI electrodes. The results of SEM and TEM showed that spherical-like nanoparticles of ZnS were uniformly distributed on the g-C3N4 sheet. The g-C3N4 phase facilitates the ZnS particles precipitate and restrain their agglomeration, which contributes to a high specific surface area of ZnS. Furthermore, the electrochemical test results indicated that ZnS/g-C3N4 composite had a good capacitance characteristic, low resistance, and high electrochemical stability. Finally, the desalinization performance of the ZnS/g-C3N4 composite electrodes was tested in traditional mode and membrane capacitive deionization (MCDI) mode. The results showed that ZnS/g-C3N4//ZnS/g-C3N4 (MCDI) exhibited an optimal desalination capacity. The adsorption amount was 27.65, 50.26, and 65.34 mg/g for NaCl initial concentration of 200, 400, and 600 mg/L, respectively, with the voltage of 1.2 V and flow rate of 5 mL/min. Increasing initial concentration enhanced the conductivity and ion migration rate so as to increase the NaCl adsorption amount. ZnS/g-C3N4 composite can be used as potential electrode material for high performance of MCDI.

Polymorph Engineering for Boosted Volumetric Na-Ion and Li-Ion Storage

To meet the ever-growing demand for advanced rechargeable batteries with light weight and compact size, much effort has been devoted to improving the volumetric capacity of electrodes. Herein, an effective strategy of polymorph engineering is proposed to boost the volumetric capacity of FeSe. Owing to the inherent metallic electronic conductivity of tetragonal-FeSe, a conductive additive-free electrode (hereafter denoted as CA-free) can be assembled with an enhanced sodium storage volumetric capacity of 1011 mAh cm^-3 , significantly higher than semiconducting hexagonal-FeSe. Impressively, the CA-free electrode can achieve an extremely high active material utilization of 96.7 wt% and high initial Coulombic efficiency of 96%, superior to most of the anodes for Na-ion storage. Moreover, the design methodology is branched out using tetragonal FeSe as the cathode for Li-ion batteries. The CA-free tetragonal-FeSe electrode can achieve a high volumetric energy density of 1373 Wh L^-1 and power density of 7200 W L^-1 , outperforming most metal chalcogenides. Reversible conversion reactions are revealed by in situ XRD for both sodium and lithium systems. The proposed design strategy provides new insight and inspiration to aid in the ongoing quest for better electrode materials.

Functionalized N-Doped Carbon Nanotube Arrays: Novel Binder-Free Anodes for Sodium-Ion Batteries

Boosting electrochemical sodium storage properties is achieved by utilizing functionalized N-doped carbon nanotube arrays (NCNAs) as anode materials. The NCNA anodes are first fabricated by self-polymerization of dopamine on cobalt hydroxide nanorod arrays as the template. The NCNAs with diameters of 100-120 nm are grown vertically to Ni foam, forming self-supported nanotube arrays. Such a structure has attractive advantages including large porosity and surface area, good electrical conductivity and mechanical strength. Consequently, the NCNAs are demonstrated to achieve excellent sodium storage performances with high capacity (335 mA h g^-1 at 100 mA g^-1), good rate capability (140 mA h g^-1 at 2 A g^-1), and superior capacity retention of 90.9% after 500 cycles. Especially, high performance is verified in the assembled full cells by using an NCNA anode and Na₃V₂(PO₄)₃/C cathode. The developed synthetic strategy provides an effective approach for the fabrication of advanced heteroatom-doped carbon-based electrodes for electrochemical energy storage.