Performance and Stability Improvement of Layered NCM Lithium-Ion Batteries at High Voltage by a Microporous Al2O3 Sol-Gel Coating.

A simple and low-cost polymer-aided sol-gel method was developed to prepare γ-Al2O3 protective layers for LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode materials. The selected polyvinyl alcohol polymer additive not only facilitates the formation of a uniform and thin γ-Al2O3 layer on the irregular and rough cathode particle surface to protect it from corrosion but also serves as a pore-forming agent to generate micropores in the film after sintering to allow fast transport of lithium ions, which guaranteed the excellent and stable battery performance at high working voltage. Detailed studies in the full battery mode showed that the leached corrosion species from the cathode had a more profound harmful effect to the graphite anode, which seemed to be the dominating factor that caused the battery performance decay.

Functional Two-Dimensional Coordination Polymeric Layer as a Charge Barrier in Li-S Batteries.

Ultrathin two-dimensional (2D) polymeric layers are capable of separating gases and molecules based on the reported size exclusion mechanism. What is equally important but missing today is an exploration of the 2D layers with charge functionality, which enables applications using the charge exclusion principle. This work demonstrates a simple and scalable method of synthesizing a free-standing 2D coordination polymer Zn2(benzimidazolate)2(OH)2 at the air-water interface. The hydroxyl (-OH) groups are stoichiometrically coordinated and implement electrostatic charges in the 2D structures, providing powerful functionality as a charge barrier. Electrochemical performance of the Li-S battery shows that the Zn2(benzimidazolate)2(OH)2 coordination polymer layers efficiently mitigate the polysulfide shuttling effects and largely enhance the battery capacity and cycle performance. The synthesis of the proposed coordination polymeric layers is simple, scalable, cost saving, and promising for practical use in batteries.

Scalable Approach To Construct Free-Standing and Flexible Carbon Networks for Lithium-Sulfur Battery.

Reconstructing carbon nanomaterials (e.g., fullerene, carbon nanotubes (CNTs), and graphene) to multidimensional networks with hierarchical structure is a critical step in exploring their applications. Herein, a sacrificial template method by casting strategy is developed to prepare highly flexible and free-standing carbon film consisting of CNTs, graphene, or both. The scalable size, ultralight and binder-free characteristics, as well as the tunable process/property are promising for their large-scale applications, such as utilizing as interlayers in lithium-sulfur battery. The capability of holding polysulfides (i.e., suppressing the sulfur diffusion) for the networks made from CNTs, graphene, or their mixture is pronounced, among which CNTs are the best. The diffusion process of polysulfides can be visualized in a specially designed glass tube battery. X-ray photoelectron spectroscopy analysis of discharged electrodes was performed to characterize the species in electrodes. A detailed analysis of lithium diffusion constant, electrochemical impedance, and elementary distribution of sulfur in electrodes has been performed to further illustrate the differences of different carbon interlayers for Li-S batteries. The proposed simple and enlargeable production of carbon-based networks may facilitate their applications in battery industry even as a flexible cathode directly. The versatile and reconstructive strategy is extendable to prepare other flexible films and/or membranes for wider applications.

Substrate Lattice-Guided Seed Formation Controls the Orientation of 2D Transition-Metal Dichalcogenides.

Two-dimensional (2D) transition-metal dichalcogenide (TMDC) semiconductors are important for next-generation electronics and optoelectronics. Given the difficulty in growing large single crystals of 2D TMDC materials, understanding the factors affecting the seed formation and orientation becomes an important issue for controlling the growth. Here, we systematically study the growth of molybdenum disulfide (MoS2) monolayer on c-plane sapphire with chemical vapor deposition to discover the factors controlling their orientation. We show that the concentration of precursors, that is, the ratio between sulfur and molybdenum oxide (MoO3), plays a key role in the size and orientation of seeds, subsequently controlling the orientation of MoS2 monolayers. High S/MoO3 ratio is needed in the early stage of growth to form small seeds that can align easily to the substrate lattice structures, while the ratio should be decreased to enlarge the size of the monolayer at the next stage of the lateral growth. Moreover, we show that the seeds are actually crystalline MoS2 layers as revealed by high-resolution transmission electron microscopy. There exist two preferred orientations (0° or 60°) registered on sapphire, confirmed by our density functional theory simulation. This report offers a facile technique to grow highly aligned 2D TMDCs and contributes to knowledge advancement in growth mechanism.

Multilayer Approach for Advanced Hybrid Lithium Battery.

Conventional intercalated rechargeable batteries have shown their capacity limit, and the development of an alternative battery system with higher capacity is strongly needed for sustainable electrical vehicles and hand-held devices. Herein, we introduce a feasible and scalable multilayer approach to fabricate a promising hybrid lithium battery with superior capacity and multivoltage plateaus. A sulfur-rich electrode (90 wt % S) is covered by a dual layer of graphite/Li4Ti5O12, where the active materials S and Li4Ti5O12 can both take part in redox reactions and thus deliver a high capacity of 572 mAh gcathode(-1) (vs the total mass of electrode) or 1866 mAh gs(-1) (vs the mass of sulfur) at 0.1C (with the definition of 1C = 1675 mA gs(-1)). The battery shows unique voltage platforms at 2.35 and 2.1 V, contributed from S, and 1.55 V from Li4Ti5O12. A high rate capability of 566 mAh gcathode(-1) at 0.25C and 376 mAh gcathode(-1) at 1C with durable cycle ability over 100 cycles can be achieved. Operando Raman and electron microscope analysis confirm that the graphite/Li4Ti5O12 layer slows the dissolution/migration of polysulfides, thereby giving rise to a higher sulfur utilization and a slower capacity decay. This advanced hybrid battery with a multilayer concept for marrying different voltage plateaus from various electrode materials opens a way of providing tunable capacity and multiple voltage platforms for energy device applications.

Microwave-Assisted Synthesis of Highly Dispersed PtCu Nanoparticles on Three-Dimensional Nitrogen-Doped Graphene Networks with Remarkably Enhanced Methanol Electrooxidation.

A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.