MXene-Bimetallic Hybrids via Mixed Molten Salts Etching for Kinetics-Enhanced and Dendrite-Free Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries with high theoretical energy density (2600 Wh kg-1) are considered to be one of the most promising secondary batteries. However, the practical application of Li-S batteries is limited by the polysulfides shuttling and unstable lithium metal anodes. Herein, an asymmetric separator (CACNM@PP), composed of Co-Ni/MXene (CNM) on the cathode and Cu-Ag/MXene (CAM) on the anode for high-performance Li-S batteries is reported. For the cathode, CNM provides a synergistic effect by integrating Co, Ni, and MXene, resulting in strong chemical interactions and fast conversion kinetics for polysulfides. For the anode, CAM with abundant lithiophilicity active sites can lower the nucleation barrier of Li. Moreover, LiCl/LiF layers are generated in situ as an ion conductor layer during charging and discharging, inducing a uniform deposition of Li. Therefore, the assembled cells with the CACNM@PP separators harvest excellent electrochemical performance. This work provides novel insights into the development of commercially available high-energy density Li-S batteries with asymmetric separators.

Interfacial Engineering of Ru Nanocluster-Modified TiO2 Nanotube-Assisted Regulation of Lithium Polysulfide Reactions.

The inhibition of lithium polysulfide (LiPS) diffusion and the acceleration of reaction kinetics are two major challenges for the practical application of lithium-sulfur (Li-S) batteries. Herein, through an interface engineering strategy, a multifunctional sulfur host based on Ru nanocluster-modified TiO2 nanotubes (TiO2-Ru) was designed. The TiO2-Ru interface field effect, combined with the hollow nanotube structure and the strong chemical action of TiO2, enhanced the LiPS trapping ability and inhibited the "shuttle effect". Furthermore, the high catalytic activity of Ru nanoclusters reduced the energy barrier of multistep LiPS reactions, thus speeding up the electrode kinetics. As a result, the TiO2-Ru-based composite sulfur cathode delivered excellent electrochemical performance, including an extremely low capacity loss of ∼0.015% per cycle and an increased areal capacity of ∼6.1 mAh cm-2 at 4.8 mg cm-2. This work contributes to a better sulfur cathode design from insights into morphology and phase interface engineering.

Furnishing Continuous Efficient Bidirectional Polysulfide Conversion for Long-Life and High-Loading Lithium-Sulfur Batteries via the Built-In Electric Field.

Most catalysts cannot accelerate uninterrupted conversion of polysulfides, resulting in poor long-cycle and high-loading performance of lithium-sulfur (Li-S) batteries. Herein, rich p-n junction CoS2 /ZnS heterostructures embedded on N-doped carbon nanosheets are fabricated by ion-etching and vulcanization as a continuous and efficient bidirectional catalyst. The p-n junction built-in electric field in the CoS2 /ZnS heterostructure not only accelerates the transformation of lithium polysulfides (LiPSs), but also promotes the diffusion and decomposition for Li2 S the from CoS2 to ZnS avoiding the aggregation of lithium sulfide (Li2 S). Meanwhile, the heterostructure possesses a strong chemisorption ability to anchor LiPSs and superior affinity to induce homogeneous Li deposition. The assembled cell with a CoS2 /ZnS@PP separator delivers a cycling stability with a capacity decay of 0.058% per cycle at 1.0 C after 1000 cycles, and a decent areal capacity of 8.97 mA h cm-2 at an ultrahigh sulfur mass loading of 6 mg cm-2 . This work reveals that the catalyst continuously and efficiently converts polysulfides via abundant built-in electric fields to promote Li-S chemistry.

Construction of Co3 O4 /ZnO Heterojunctions in Hollow N-Doped Carbon Nanocages as Microreactors for Lithium-Sulfur Full Batteries.

Lithium-sulfur (Li-S) batteries are promising alternatives of conventional Li-ion batteries attributed to their remarkable energy densities and high sustainability. However, the practical applications of Li-S batteries are hindered by the shuttling effect of lithium polysulfides (LiPSs) on cathode and the Li dendrite formation on anode, which together leads to inferior rate capability and cycling stability. Here, an advanced N-doped carbon microreactors embedded with abundant Co3 O4 /ZnO heterojunctions (CZO/HNC) are designed as dual-functional hosts for synergistic optimization of both S cathode and Li metal anode. Electrochemical characterization and theoretical calculations confirm that CZO/HNC exhibits an optimized band structure that effectively facilitates ion diffusion and promotes bidirectional LiPSs conversion. In addition, the lithiophilic nitrogen dopants and Co3O4/ZnO sites together regulate dendrite-free Li deposition. The S@CZO/HNC cathode exhibits excellent cycling stability at 2 C with only 0.039% capacity fading per cycle over 1400 cycles, and the symmetrical Li@CZO/HNC cell enables stable Li plating/striping behavior for 400 h. Remarkably, Li-S full cell using CZO/HNC as both cathode and anode hosts shows an impressive cycle life of over 1000 cycles. This work provides an exemplification of designing high-performance heterojunctions for simultaneous protection of two electrodes, and will inspire the applications of practical Li-S batteries.

Electrochemical Resistive Switching in Nanoporous Hybrid Films by One-Step Molecular Layer Deposition.

An organic-inorganic hybrid resistive random-access memory based on a nanoporous zinc-based hydroquinone (Zn-HQ) thin film has been constructed with a Pt/Zn-HQ/Ag sandwich structure. The porous Zn-HQ functional layer was directly fabricated by a one-step molecular layer deposition. These Pt/Zn-HQ/Ag devices show a typical electroforming-free bipolar resistive switching characteristic with lower operation voltages and higher on/off ratio above 102. Our nanoporous hybrid devices can also realize multilevel storage capability and exhibit excellent endurance/retention properties. The connection and disconnection of Ag conductive filaments in nanoporous Zn-HQ thin film follow the electrochemical metallization mechanism. Our computational simulations confirm that the existence of nanopores in Zn-HQ thin films facilitates the Ag filament formation, contributing to the high performance of our hybrid devices.

Cu2O/SrTi1-xCrxO3 Heterojunction Photocatalyst for the Efficient Degradation of Isopropanol under Visible Light Irradiation.

A heterojunction of Cu2O and Cr-doped SrTiO3 (SrTi1-xCrxO3) was designed for selective photocatalytic isopropanol (IPA) oxidation under visible light irradiation. The photocatalytic oxidation of IPA was measured in a fixed-bed reactor. Cr dopants can increase the light absorption and improve the activity of the catalyst. The formation of the Cu2O/SrTi1-xCrxO3 heterojunction can further broaden the absorption range of lights and dramatically increase the photocatalytic activity for selective oxidation of IPA. The 3% Cu2O/SrTi0.99Cr0.01O3 catalyst can fully convert ∼1000 ppm IPA under illumination in 2 h. The selectivity of acetone is ∼100%. The yield is 83 and 4 times higher than that using SrTiO3 and SrTi0.99Cr0.01O3 as catalysts, respectively. By measuring the ultraviolet-visible absorption spectra and Mott-Schottky plots, we obtained the band structure of the heterojunction, which shows that the conduction and valence bands of Cu2O are higher than those of SrTi1-xCrxO3, therefore facilitating the separation and transfer of photogenerated electrons and holes. In addition, electron paramagnetic resonance spectroscopy and radical trapping tests reveal that the generation of hydroxyl and superoxide leads to photocatalytic oxidation of IPA by the heterojunction photocatalyst.

In Situ Formation of Polycyclic Aromatic Hydrocarbons as an Artificial Hybrid Layer for Lithium Metal Anodes.

Nonuniform Li deposition causes dendrites and low Coulombic efficiency (CE), seriously hindering the practical applications of Li metal. Herein, we developed an artificial solid-state interphase (SEI) with planar polycyclic aromatic hydrocarbons (PAHs) on the surface of Li metal anodes by a facile in situ formation technology. The resultant dihydroxyviolanthron (DHV) layers serve as the protective layer to stabilize the SEI. In addition, the oxygen-containing functional groups in the soft and conformal SEI film can regulate the diffusion and transport of Li ions to homogenize the deposition of Li metal. The artificial SEI significantly improves the CEs and shows superior cyclability of over 1000 h at 4 mAh cm-2. The LiFePO4/Li cell (2.8 mAh cm-2) enables a long cyclability for 300 cycles and high CEs of 99.8%. This work offers a new strategy to inhibit Li dendrite growth and enlightens the design on stable SEI for metal anodes.

Tailoring Stress and Ion-Transport Kinetics via a Molecular Layer Deposition-Induced Artificial Solid Electrolyte Interphase for Durable Silicon Composite Anodes.

Silicon is considered as a blooming candidate material for next-generation lithium-ion batteries due to its low electrochemical potential and high theoretical capacity. However, its commercialization has been impeded by the poor cycling issue associated with severe volume changes (∼380%) upon (de)lithiation. Herein, an organic-inorganic hybrid film of titanicone via molecular layer deposition (MLD) is proposed as an artificial solid electrolyte interphase (SEI) layer for Si anodes. This rigid-soft titanicone coating with Young's modulus of 21 GPa can effectively relieve stress concentration during the lithiation process, guaranteeing the stability of the mechanical structure of a Si nanoparticles (NPs)@titanicone electrode. Benefiting from the long-strand (Ti-O-benzene-O-Ti-) unit design, the optimized Si NPs@70 cycle titanicone anode delivers a high Li+ diffusion coefficient and a low Li+ diffusion barrier, as revealed by galvanostatic intermittent titration (GITT) investigations and density functional theory (DFT) simulations, respectively. Ultimately, the Si NPs@70 cycle titanicone electrode shows high initial Coulombic efficiency (84%), long cycling stability (957 mAh g-1 after 450 cycles at 1 A g-1), a stable SEI layer, and good rate performances. The molecular-scale design of the titanicone-protected Si anodes may bring in new opportunities to realize the next-generation lithium-ion batteries as well as other rechargeable batteries.

Electrochemical Fabrication of Monolithic Electrodes with Core/Shell Sandwiched Transition Metal Oxide/Oxyhydroxide for High-Performance Energy Storage.

Transition metal oxides/oxyhydroxides (TMOs) are promising high-capacity materials for electrochemical energy storage. However, the low rate and poor cyclability hinder practical applications. In this work, we developed a general electrochemical route to fabricate monolithic core/shell sandwiched structures, which are able to significantly improve the electrochemical properties of TMO electrodes by electrically wiring the insulating active materials and alleviating the adverse effects caused by volume changes using engineered porous structures. As an example, a lithium ion battery anode of porous MnO sandwiched between CNT and carbon demonstrates a high capacity of 554 mAh g-1 even after 1000 cycles at 2 A g-1. An all-solid-state symmetric pseudocapacitor consisting of CNT@MnOOH@polypyrrole exhibits a high specific capacitance of 148 F g-1 and excellent capacitance retention (92% after 10000 cycles at 2 A g-1). Several other examples and applications have further confirmed the effectiveness of improving the electrochemical properties by core/shell sandwiched structures.