Xin-Gai Wang

In situ sulfur deposition route to obtain sulfur–carbon composite cathodes for lithium–sulfur batteries

An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S–CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g−1 at the current density of 160 mA g−1, respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g−1 with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium–sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S–CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging–discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur–carbon composite cathodes for rechargeable lithium–sulfur batteries.

NiFe2O4–CNT composite: an efficient electrocatalyst for oxygen evolution reactions in Li–O2 batteries guided by computations

Lithium–oxygen batteries are regarded as the most promising candidate for future energy storage systems. However, their poor rechargeability and low efficiency remain critical barriers for practical applications. By using first-principles computations, we disclosed that NiFe2O4 has superior oxygen evolution reaction (OER) activity for the decomposition of Li2O2. Guided by computations, we prepared a composite of NiFe2O4 and carbon nanotubes (CNTs) through a hydrothermal route and applied it to Li–O2 batteries. The batteries with NiFe2O4–CNT air cathodes displayed lower charging overpotential and better cycling performance than those with CNT air cathodes. The improved electrochemical performance was attributed to the high OER activity of NiFe2O4 for the decomposition of Li2O2.

Verifying the Rechargeability of Li‐CO2 Batteries on Working Cathodes of Ni Nanoparticles Highly Dispersed on N‐Doped Graphene

Abstract Li‐CO2 batteries could skillfully combine the reduction of “greenhouse effect” with energy storage systems. However, Li‐CO2 batteries still suffer from unsatisfactory electrochemical performances and their rechargeability is challenged. Here, it is reported that a composite of Ni nanoparticles highly dispersed on N‐doped graphene (Ni‐NG) with 3D porous structure, exhibits a superior discharge capacity of 17 625 mA h g−1, as the air cathode for Li‐CO2 batteries. The batteries with these highly efficient cathodes could sustain 100 cycles at a cutoff capacity of 1000 mA h g−1 with low overpotentials at the current density of 100 mA g−1. Particularly, the Ni‐NG cathodes allow to observe the appearance/disappearance of agglomerated Li2CO3 particles and carbon thin films directly upon discharge/charge processes. In addition, the recycle of CO2 is detected through in situ differential electrochemical mass spectrometry. This is a critical step to verify the electrochemical rechargeability of Li‐CO2 batteries. Also, first‐principles computations further prove that Ni nanoparticles are active sites for the reaction of Li and CO2, which could guide to design more advantageous catalysts for rechargeable Li‐CO2 batteries.

High performance Li–CO2 batteries with NiO–CNT cathodes

Rechargeable Li–CO2 batteries are promising energy storage systems for reducing fossil fuel consumption and mitigating the “greenhouse effect” due to the use of a reversible reaction between lithium and CO2. However, current Li–CO2 batteries still suffer from several unresolved problems such as high charge potential and low coulombic efficiency, and hence more efforts are required to optimize their electrochemical performance. In this work, a composite of sheet-like NiO dispersed on carbon nanotubes was prepared via a solvothermal method. The composite was employed as an efficient air cathode for Li–CO2 batteries, with very high coulombic efficiency (97.8%) and good cycling stability (40 cycles). This study provides new strategies to develop cheap and abundant catalysts to improve the performance of Li–CO2 batteries.

Fixing of highly soluble Br2/Br− in porous carbon as a cathode material for rechargeable lithium ion batteries

LiBr, as a representative of highly soluble electrochemically active materials, is fixed in nanopores of conductive carbon black (CCB). The Li/LiBr–CCB battery exhibits excellent high-rate capability to avoid slow solid-phase diffusion of Li ions in traditional solid cathode materials. The success will broaden the range of alternative materials for cathodes in LIBs and make them capable of providing both high power density and energy density.

Fabricating Ir/C Nanofiber Networks as Free-Standing Air Cathodes for Rechargeable Li-CO2 Batteries

Li-CO2 batteries are promising energy storage systems by utilizing CO2 at the same time, though there are still some critical barriers before its practical applications such as high charging overpotential and poor cycling stability. In this work, iridium/carbon nanofibers (Ir/CNFs) are prepared via electrospinning and subsequent heat treatment, and are used as cathode catalysts for rechargeable Li-CO2 batteries. Benefitting from the unique porous network structure and the high activity of ultrasmall Ir nanoparticles, Ir/CNFs exhibit excellent CO2 reduction and evolution activities. The Li-CO2 batteries present extremely large discharge capacity, high coulombic efficiency, and long cycling life. Moreover, free-standing Ir/CNF films are used directly as air cathodes to assemble Li-CO2 batteries, which show high energy density and ultralong operation time, demonstrating great potential for practical applications.