Weiqiang Lv

From Metal–Organic Framework to Li2S@C–Co–N Nanoporous Architecture: A High-Capacity Cathode for Lithium–Sulfur Batteries

Owing to the high theoretical specific capacity (1166 mAh g-1), lithium sulfide (Li2S) has been considered as a promising cathode material for Li-S batteries. However, the polysulfide dissolution and low electronic conductivity of Li2S limit its further application in next-generation Li-S batteries. In this report, a nanoporous Li2S@C-Co-N cathode is synthesized by liquid infiltration-evaporation of ultrafine Li2S nanoparticles into graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) derived from metal-organic frameworks. The obtained Li2S@C-Co-N architecture remarkably immobilizes Li2S within the cathode structure through physical and chemical molecular interactions. Owing to the synergistic interactions between C-Co-N and Li2S nanoparticles, the Li2S@C-Co-N composite delivers a reversible capacity of 1155.3 (99.1% of theoretical value) at the initial cycle and 929.6 mAh g-1 after 300 cycles, with nearly 100% Coulombic efficiency and a capacity fading of 0.06% per cycle. It exhibits excellent rate capacities of 950.6, 898.8, and 604.1 mAh g-1 at 1C, 2C, and 4C, respectively. Such a cathode structure is promising for practical applications in high-performance Li-S batteries.

Three-Dimensional Hierarchical Reduced Graphene Oxide/Tellurium Nanowires: A High-Performance Freestanding Cathode for Li–Te Batteries

Three-dimensional aerogel with ultrathin tellurium nanowires (TeNWs) wrapped homogeneously by reduced graphene oxide (rGO) is realized via a facile hydrothermal method. Featured with high conductivity and large flexibility, the rGO constructs a conductive three-dimensional (3D) backbone with rich porosity and leads to a free-standing, binder-free cathode for lithium-tellurium (Li-Te) batteries with excellent electrochemical performances. The cathode shows a high initial capacity of 2611 mAh cm(-3) at 0.2 C, a high retention of 88% after 200 cycles, and a high-rate capacity of 1083 mAh cm(-3) at 10 C. In particular, the 3D aerogel cathode delivers a capacity of 1685 mAh cm(-3) at 1 C after 500 cycles, showing pronounced long-cycle performance at high current density. The performances are attributed to the well-defined flexible 3D architecture with high porosity and conductivity network, which offers highly efficient channels for electron transfer and ionic diffusion while compromising volume expansion of Te in charge/discharge. Owing to such advantageous properties, the reported 3D rGO/tellurium nanowire (3DGT) aerogel presents promising application potentials as a high-performance cathode for Li-Te batteries.

Interfacial lattice-strain effects on improving the overall performance of micro-solid oxide fuel cells

Interfacial lattice-strain, typically capable of altering the energy states of electrical carriers associated with hetero-interfaces, has shown unprecedented efficiency for improving the performance of a variety of real-life devices involving heterostructure crystals, including fuel cells and batteries. In this review, we overview recent findings on interfacial lattice-strain effects on improving ionic conductivity, oxygen vacancy formation, and surface oxygen exchange kinetics at cathodes of micro-solid oxide fuel cells. Our review seeks to provide evidence of interfacial strain effects on the overall performance of solid oxide fuel cells, highlight the fundamental and technological relevance, and provide insightful guidelines to enable the operation of micro-solid oxide fuel cells at lower temperatures more efficiently by tailoring the lattice-strain.

Tellurium-Impregnated Porous Cobalt-Doped Carbon Polyhedra as Superior Cathodes for Lithium–Tellurium Batteries

Lithium-tellurium (Li-Te) batteries are attractive for energy storage owing to their high theoretical volumetric capacity of 2621 mAh cm-3. In this work, highly nanoporous cobalt and nitrogen codoped carbon polyhedra (C-Co-N) derived from a metal-organic framework (MOF) is synthesized and employed as tellurium host for Li-Te batteries. The Te@C-Co-N cathode with a high Te loading of 77.2 wt % exhibits record-breaking electrochemical performances including an ultrahigh initial capacity of 2615.2 mAh cm-3 approaching the theoretical capacity of Te (2621 mAh cm-3), a superior cycling stability with a high capacity retention of 93.6%, a ∼99% Columbic efficiency after 800 cycles as well as rate capacities of 2160, 1327.6, and 894.8 mAh cm-3 at 4, 10, and 20 C, respectively. The redox chemistry of tellurium is revealed by in operando Raman spectroscopic analysis and density functional theory simulations. The results illustrate that the performances are attributed to the highly conductive C-Co-N matrix with an advantageous structure of abundant micropores, which provides highly efficient channels for electron transfer and ionic diffusion as well as sufficient surface area to efficiently host tellurium while mitigating polytelluride dissolution and suppressing volume expansion.

An Energy Investigation into 1D/2D Oriented‐Attachment Assemblies of 1D Ag Nanocrystals

In the field of oriented-attachment crystal growth, one-dimensional nanocrystals are frequently employed as building blocks to synthesize two-dimensional or large-aspect-ratio one-dimensional nanocrystals. Despite recent extensive experimental advances, the underlying inter-particle interaction in the synthesis still remains elusive. In this report, using Ag as a platform, we investigate the van der Waals interactions associated with the side-by-side and end-to-end assemblies of one-dimensional nanorods. The size, aspect ratio, and inter-particle separation of the Ag precursor nanorods are found to have dramatically different impacts on the van der Waals interactions in the two types of assemblies. Our work facilitates the fundamental understanding of the oriented-attachment assembling mechanism based on one-dimensional nanocrystals.

Oriented-attachment dimensionality build-up via van der Waals interaction

In this study, molecular static calculation is carried out to evaluate the van der Waals interaction (vdW) associated with different oriented attachment (OA) growth systems involving 1D nanorods (NRs), 2D nanoplates (NPts) and 3D nanostructures (NSts) for the first time. Our results show that the vdW is, to a large extent, determined by the attaching area at all OA growth stages of nanocrystals. The vdW increases significantly as the OA growth varies from 1D NR–NP, end-to-end NR–NR assemblies to 2D side-by-side NR–NR/3D NPt–NPt assemblies. Our study reveals the fundamental details in vdW, one of the governing inter-particle interactions involved in OA growth of NCs, and facilitates the analytical understanding of the OA growth thermodynamics.

Gas Diffusion Mechanisms and Models

The one-dimensional diffusion of gas molecules in porous media involves molecular interactions between gas molecules as well as collisions between gas molecules and the porous media (Joshi et al. in J. Phys. D Appl. Phys. 40:7593–7600, 2007 [1], Cannarozzo et al. in J. Appl. Electrochem. 38:1011–1018, 2008 [2], Veldsink et al. in Chem. Eng. J. Biochem. Eng. J. 57:115–125, 1995 [3]).

A Single-Step Hydrothermal Route to 3D Hierarchical Cu2O/CuO/rGO Nanosheets as High-Performance Anode of Lithium-Ion Batteries

As anodes of Li-ion batteries, copper oxides (CuO) have a high theoretical specific capacity (674 mA h g-1 ) but own poor cyclic stability owing to the large volume expansion and low conductivity in charges/discharges. Incorporating reduced graphene oxide (rGO) into CuO anodes with conventional methods fails to build robust interaction between rGO and CuO to efficiently improve the overall anode performance. Here, Cu2 O/CuO/reduced graphene oxides (Cu2 O/CuO/rGO) with a 3D hierarchical nanostructure are synthesized with a facile, single-step hydrothermal method. The Cu2 O/CuO/rGO anode exhibits remarkable cyclic and high-rate performances, and particularly the anode with 25 wt% rGO owns the best performance among all samples, delivering a record capacity of 550 mA h g-1 at 0.5 C after 100 cycles. The pronounced performances are attributed to the highly efficient charge transfer in CuO nanosheets encapsulated in rGO network and the mitigated volume expansion of the anode owing to its robust 3D hierarchical nanostructure.

Space matters: Li+ conduction versus strain effect at FePO4/LiFePO4 interface

FePO4/LiFePO4 (FP/LFP) interfacial strain, giving rise to substantial variation in interfacial energy and lattice volume, is inevitable in the (de)lithiation process of LiFePO4, a prototype of Li ion batterycathodes. Extensive theoretical and experimental research has been focused on the effect of lattice strain energy on FP/LFP interface propagation orientation and cyclic stability of the electrode. However, the essential effect of strain induced lattice distortion on Li+ transport at the FP/LFP interface is typically overlooked. In this report, a coherent interface model is derived to evaluate quantitatively the correlation between FP/LFP lattice distortion and Li+conduction. The results illustrate that the effect of lattice strain on Li+conduction depends strongly on FP/LFP interface orientations. Lattice strain induces a 90% decrease of Li+conductivity in ac-plane oriented (de)lithiation at room temperature. The opposite effect of lattice strain on delithiation and lithiation for ab- and bc-orientations is elucidated. In addition, the effect of lattice strain tends to be more pronounced at a lower working temperature. This study provides an efficient platform to comprehend and manipulate Li+conduction in the charge and discharge of lithium ion batteries, the large-scale application of which is frequently challenged by limited in-cell ion conduction.

Direct impregnation of SeS2 into a MOF-derived 3D nanoporous Co–N–C architecture towards superior rechargeable lithium batteries

Metal–organic framework (MOF) derived cobalt- and nitrogen-doped porous carbon (Co–N–C) polyhedra are employed, for the first time, as SeS2 immobilizers (Co–N–C/SeS2). As the cathode of lithium–sulfur (Li–S) batteries, the Co–N–C/SeS2 composite with a high loading (66.5 wt%) of SeS2 delivers a reversible capacity of 1165.1 mA h g−1 and an over 84.1% capacity retention of the initial capacity (970.2 mA h g−1) with a nearly 100% coulombic efficiency after 200 cycles. The Co–N–C/SeS2 cathode shows excellent rate performances with capacities of 760 mA h g−1, 604.1 mA h g−1, and 439.7 mA h g−1 at 1C, 2C, and 4C, respectively. The redox chemistry of SeS2 is revealed by in situ Raman spectroscopic analysis and density functional theory (DFT) simulations. The superior electrochemical performance of the cathode is attributed to the unique Co–N–C structure with abundant micropores and uniformly-embedded ultrafine Co nanoparticles, which provide abundant SeS2 absorption and catalytically active sites and efficiently prevent the dissolution of polysulfides and polyselenides. The conductive Co–N–C framework facilitates fast electron and ion transfer in electrochemical reactions. Our work facilitates the development of high-performance cathodes for Li–S batteries.