Two-Dimensional CeO2/RGO Composite-Modified Separator for Lithium/Sulfur Batteries

MOF-Derived CeO2 Nanorod as a Separator Coating Enabling Enhanced Performance for Lithium-Sulfur Batteries

The deployment of Li-S batteries in the commercial sector faces obstacles due to their low electrical conductivity, slow redox reactions, quick fading of capacity, and reduced coulombic efficiency. These issues stem from the "shuttle effect" associated with lithium polysulfides (LiPSs). In this work, a haystack-like CeO2 derived from a cerium-based metal-organic framework (Ce-MOF) is obtained for the modification of a polypropylene separator. The carbon framework and CeO2 coexist in this haystack-like structure and contribute to a synergistic effect on the restriction of LiPSs shuttling. The carbon network enhances electron transfer in the conversion of LiPSs, improving the rate performance of the battery. Moreover, CeO2 enhances the redox kinetics of LiPSs, effectively reducing the "shuttle effect" in Li-S batteries. The Li-S battery with the optimized CeO2 modified separator shows an initial discharge capacity of 870.7 mAh/g at 2 C, maintaining excellent capacity over 500 cycles. This research offers insights into designing functional separators to mitigate the "shuttle effect" in Li-S batteries.

Modified separators boost polysulfides adsorption-catalysis in lithium-sulfur batteries from Ni@Co hetero-nanocrystals into CNT-porous carbon dual frameworks

In this manuscript, nickel/cobalt bimetallic nanocrystals confining into three-dimensional interpenetrating dual-carbon conductive structure (NiCo@C/CNTs) were successfully manufactured by annealing its core-shell structure (Ni-ZIF-67@ZIF-8) precursor under the high temperature. The results presented that the bimetallic nickel and cobalt nanocrystals with superior catalytic activity could quickly convert solid Li2S/Li2S2into soluble LiPSs and effectively decrease the energy barrier. While the hierarchical CNT-porous carbon dual frameworks can provide quick electron/ion transport because of their large specific surface area and the exposure of enough active sites. When used as the separator modifier for lithium sulfur batteries, the battery properties were significantly improved with high specific capacity, outstanding rate capability, and long-term cycle stability. Specifically, its initial specific capacity can achieve to 1038.51 mAh g-1 at 0.5C. At the high rate of 3C, it still delivers satisfactory discharge capacity of 555 mAhg-1 and the capacity decay rate is only 0.065% per cycle after 1000 cycles at 1C. Furthermore, even exposed to heavy sulfur loading (3.61 mg/cm2), they still maintain promising cycle stability. Therefore, such kinds of MOFs derivative with powerful chemical immobilization and catalytic conversion for polysulfides provides a novel guidance for the modification separator and the potential application in the field of high-performance Li-S batteries.

Adsorption-catalysis design with cerium oxide nanorods supported nickel-cobalt-oxide with multifunctional reaction interfaces for anchoring polysulfides and accelerating redox reactions in lithium sulfur battery

The charge and discharge working mechanisms in lithium sulfur batteries contain multi-step complex reactions involving two-electron transfer and multiple phase transformations. The dissolution and diffusion of lithium polysulfides cause a huge loss of active material and fast capacity decay, preventing the practical use of lithium sulfur batteries. Herein, CeO₂ nanorods supported bimetallic nickel cobalt oxide (NiCo₂O_x) was investigated as a cathode host material for lithium sulfur batteries, which can provide adsorption-catalysis dual synergy to restrain the shuttle of polysulfides and stimulate rapid redox reaction for the conversion of polysulfides. The polar CeO₂ nanorods with abundant surface defects exhibit chemisorption towards lithium polysulfides and the excellent electrocatalytic activity of NiCo₂O_x nanoclusters can rev up the chain transformation of lithium polysulfides. The electrochemical results show that the battery with NiCo₂O_x/CeO₂ nanorods can demonstrate high discharge capacity, stable cycling, low voltage polarization and high sulfur utilization. The battery with NiCo₂O_x/CeO₂ nanorods unveils a high specific capacity of 1236 mAh g^-1 with a very low capacity fading of 0.09% per cycle after 100 cycles at a 0.2C current rate. Moreover, the excellent performance with high sulfur loading (>5 mg cm^-2) verifies a huge promise for future commercial applications.

Preparation and Characterization of Multi-Doped Porous Carbon Nanofibers from Carbonization in Different Atmospheres and Their Oxygen Electrocatalytic Properties Research

Recently, electrocatalysts for oxygen reduction reaction (ORR) as well as oxygen evolution reaction (OER) hinged on electrospun nanofiber composites have attracted wide research attention. Transition metal elements and heteroatomic doping are important methods used to enhance their catalytic performances. Lately, the construction of electrocatalysts based on metal-organic framework (MOF) electrospun nanofibers has become a research hotspot. In this work, nickel-cobalt zeolitic imidazolate frameworks with different molar ratios (Ni_xCo_y-ZIFs) were synthesized in an aqueous solution, followed by Ni_xCo_y-ZIFs/polyacrylonitrile (PAN) electrospun nanofiber precursors, which were prepared by a simple electrospinning method. Bimetal (Ni-Co) porous carbon nanofiber catalysts doped with nitrogen, oxygen, and sulfur elements were obtained at high-temperature carbonization treatment in different atmospheres (argon (Ar), Air, and hydrogen sulfide (H₂S)), respectively. The morphological properties, structures, and composition were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Moreover, the specific surface area of materials and their pore size distribution was characterized by Brunauer-Emmett-Teller (BET). Linear sweep voltammetry curves investigated catalyst performances towards oxygen reduction and evolution reactions. Importantly, Ni₁Co₂-ZIFs/PAN-Ar yielded the best ORR activity, whereas Ni₁Co₁-ZIFs/PAN-Air exhibited the best OER performance. This work provides significant guidance for the preparation and characterization of multi-doped porous carbon nanofibers carbonized in different atmospheres.

Cerium oxide nanorods anchored on carbon nanofibers derived from cellulose paper as effective interlayer for lithium sulfur battery

Investigation of sluggish redox kinetics and polysulfide shuttling is crucial to design advanced lithium sulfur battery. Cerium oxide (CeO₂) has remarkable polysulfide adsorption capability and has been recently investigated in lithium sulfur battery application. With the goal of bridging towards commercialization of lithium sulfur battery, cellulose paper derived carbon fiber decorated with CeO₂ nanorods using hydrothermal method has been fabricated and used as interlayer material for lithium sulfur battery. In this novel design, the carbon fiber provides physical confinement with its 3-D interconnected conductive structure and CeO₂ adsorbs lithium polysulfides chemically to reduce shuttle effect to achieve long lifetime and high capacity for lithium sulfur battery. With a sulfur content of 2 mg, a high capacity of 1177 mAhg^-1 was achieved at 0.2C with an excellent stability of only 0.11% capacity decay per cycle over 300 cycles. The improved performance is attributed to the binding of lithium polysulfides by CeO₂ and the blocking of polysulfides physically by the compact conducting carbon fiber.

A novel battery separator coated by a europium oxide/carbon nanocomposite enhances the performance of lithium sulfur batteries

Lithium sulfur (Li-S) batteries represent one of the most promising future power batteries due to their remarkable advantages of low cost and ultrahigh theoretical energy density. However, the commercial applications of Li-S batteries have long been plagued by the shuttling effect of polysulfides and sluggish redox kinetics of these species. Herein, we designed a novel battery separator coated by a europium oxide-doped porous Ketjen Black (Eu₂O₃/KB) and tested its performance for the Li-S batteries for the first time. Experimental results and theoretical calculations reveal that the improved electrochemical performance can be attributed to the presence of Eu₂O₃. The strong binding effect between Eu₂O₃ and polysulfides is demonstrated in two aspects: (1) there exist strong interactions between Eu₂O₃ as a Lewis acid and polysulfides of strong Lewis basicity; (2) Eu₂O₃ with oxygen-vacancy defects provides active sites for catalyzing polysulfide conversion and polysulfide trapping. Thus, a Li-S battery with the Eu₂O₃/KB modified separator delivers highly stable cycling performance and excellent rate capability, with the capacity decay ratio of merely 0.05% per cycle under 1 C rate during 500 cycles, and high specific capacity of 563 mAh g^-1 at 3 C rate. This work offers a meaningful exploration of the application of rare earth oxides for the modification of the separator towards high performance Li-S batteries.

Synthesis and catalytic evaluation of PVP-CeO2/rGO as a highly efficient and recyclable heterogeneous catalyst for multicomponent reactions in water

A highly efficient and eco-friendly route for the reduction of graphene oxide (GO) to reduced graphene oxide (rGO) was developed by using polyvinylpyrrolidone coated CeO₂ NPs (PVP-CeO₂) as a reducing and stabilizing agent. The resulting carbonaceous material, PVP-CeO₂/rGO, was well characterized with different spectroscopic techniques such as Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), elemental mapping, Transmission Electron Microscopy (TEM), Raman spectroscopy, powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), X-ray Photoelectron Spectroscopy (XPS), and Thermal Gravimetric (TG) analyses. The material exhibited high catalytic potential towards multicomponent reactions for the synthesis of biologically relevant benzodiazepine derivatives in aqueous media. The efficiency of the material for the desired reaction was shown in the form of an excellent product yield (96-98%) and a very short reaction time period (7-10 min). The use of water as solvent and recyclability of the catalyst made the present protocol acceptable from a green perspective.

Detection of Hydroxyl Radicals Using Cerium Oxide/Graphene Oxide Composite on Prussian Blue

A composite sensor consisting of two separate inorganic layers of Prussian blue (PB) and a composite of cerium oxide nanoparticles (CeNPs) and graphene oxide (GO), is tested with •OH radicals. The signals from the interaction between the composite layers and •OH radicals are characterized using cyclic voltammetry (CV). The degradation of PB in the presence of H₂O₂ and •OH radicals is observed and its impact on the sensor efficiency is investigated. The results show that the composite sensor differentiates between the solutions with and without •OH radicals by the increase of electrochemical redox current in the presence of •OH radicals. The redox response shows a linear relation with the concentration of •OH radicals where the limit of detection, LOD, is found at 60 µM (100 µM without the PB layer). When additional composite layers are applied on the composite sensor to prevent the degradation of PB layer, the PB layer is still observed to be degraded. Furthermore, the sensor conductivity is found to decrease with the additional layers of composite. Although the CeNP/GO/PB composite sensor demonstrates high sensitivity with •OH radicals at low concentrations, it can only be used once due to the degradation of PB.

Cobalt nanoparticles shielded in N-doped carbon nanotubes for high areal capacity Li–S batteries

The doped N species and embedded Co nanoparticles of Co-NCNTs have a synergistic effect on lithium polysulfide capture and conversion, leading to enhanced redox reaction kinetics.

Phosphorus-doped graphene nanosheets anchored with cerium oxide nanocrystals as effective sulfur hosts for high performance lithium-sulfur batteries

To meet the ever-increasing market requirements for energy storage devices with improved performances, lithium-sulfur (Li-S) batteries with high theoretical capacity and energy density have been extensively studied. However, to bring Li-S batteries into real life, several challenges still need to be overcome, such as dissolution of intermediate polysulfides, large volume change, and low electrical conductivity of sulfur. In this study, phosphorus-doped graphene anchored with well-dispersed cerium oxide nanocrystals (CeO₂/PG) were prepared as effective sulfur host materials through a hydrothermal synthesis method followed by a thermal treatment process. The cerium oxide nanocrystals/phosphorus-doped graphene (CeO₂/PG) nanocomposites can provide high electrical conductivity, sufficient spaces for the storage of sulfur, and strong chemical binding with polysulfides. In particular, well-dispersed polar CeO₂ nanocrystals effectively exhibit chemical affinity with polysulfides and promote polysulfide redox reactions during the cycling. Furthermore, phosphorus dopants can offer a sufficient number of active sites for polysulfide trapping and enhance the overall electrical conductivity of graphene nanosheets. As a result, a S@CeO₂/PG cathode with 72.3 wt% sulfur content exhibits a high specific capacity (1287 mA h g^-1 at 0.1 C-rate) and good cycling stability (577.7 mA h g^-1 at 1 C-rate after 100 cycles).

TiO2/Porous Carbon Composite-Decorated Separators for Lithium/Sulfur Battery

The practical application of lithium/sulfur (Li/S) batteries is hindered by the migration of soluble polysulfides (Li₂S_n, 4 ≤ n ≤ 8) from cathode to anode, leading to poor electrochemical stability of the cell. To address this issue, in the present study, a TiO₂/porous carbon (TiO₂/PC) composite-coated Celgard 2400 separator was successfully fabricated and used as a polysulfide barrier for the Li/S battery. In TiO₂/PC, the highly conductive PC with three-dimensional ordered porous structure physically constrains polysulfides and at the same time serves as an additional upper current collector. On the other hand, the TiO₂ on the surface of PC chemically adsorbed polysulfides during the charge/discharge process. Due to the physical and chemical adsorption properties of TiO₂/PC composite coating layer, an initial discharge capacity of 926 mAh g^-1 at 0.1 C and a low fading rate (75% retention after 150 cycles) were achieved. Moreover, in the rate capability test, the discharge capacity for the TiO₂/PC-modified Li/S battery was recovered to 728 mAh g^-1 at 0.1 C after high-rate cycling and remained ~ 88% of the initial reversible capacity.