All-Fluorinated Electrolyte Engineering Enables Practical Wide-Temperature-Range Lithium Metal Batteries.

The development of lithium metal batteries (LMBs) is severely hindered owing to the limited temperature window of the electrolyte, which renders uncontrolled side reactions, unstable electrolyte/electrode interface (EEI) formation, and sluggish desolvation kinetics for wide temperature operation condition. Herein, we developed an all-fluorinated electrolyte composed of lithium bis(trifluoromethane sulfonyl)imide, hexafluorobenzene (HFB), and fluoroethylene carbonate, which effectively regulates solvation structure toward a wide temperature of 160 °C (-50 to 110 °C). The introduction of thermostable HFB induces the generation of EEI with a high LiF ratio of 93%, which results in an inhibited side reaction and gas generation on EEI and enhanced interfacial ion transfer at extreme temperatures. Therefore, an unparalleled capacity retention of 88.3% after 400 cycles at 90 °C and an improved cycling performance at -50 °C can be achieved. Meanwhile, the practical 1.3 Ah-level pouch cell delivers high energy density of 307.13 Wh kg-1 at 60 °C and 277.99 Wh kg-1 at -30 °C after 50 cycles under lean E/C ratio of 2.7 g/Ah and low N/P ratio of 1.2. This work not only offers a viable strategy for wide-temperature-range electrolyte design but also promotes the practicalization of LMBs.

Enhanced near-infrared optical transmission in zinc germanium phosphide crystals via precise magnesium doping.

A zinc germanium phosphorus (ZnGeP2) crystal with a chalcopyrite structure is an efficient frequency converter in the mid-infrared region. However, point defect-induced optical absorption at the pumping wavelength (near infrared region) blocked the further application of ZnGeP2. To alleviate the absorption losses caused by point defects, in situ magnesium doping compensation was presented during the ZnGeP2 bulk crystal growth process via the vertical Bridgman method. Combined with theoretical calculations, the structural distortion of the magnesium-doped ZnGeP2 crystals in different orientations was illustrated. The thermodynamic and kinetic stability of the magnesium-doped ZnGeP2 structure were demonstrated. The transmission results indicated the improvement of transmittance within a wavelength range of 1.8-2.4 µm when doped with magnesium, which revealed the powerful ability of the appropriate dopant in optimizing near-infrared optical properties. Thus, the introduction of magnesium is a practical approach to improve the transmittance performance and extend the pumping source wavelengths of ZnGeP2 crystals.

The Numerical Simulations and Experimental Study of an 8-Inch SiC Single Crystal with Reduced BPD Density.

The basal plane dislocation (BPD) density is one of the most important defects affecting the application of SiC wafers. In this study, numerical simulations and corresponding experiments were conducted to investigate the influence of cooling processes, seed-bonding methods, and graphite crucible materials on the BPD density in an 8-inch N-type 4H-SiC single crystal grown by the physical vapor transport (PVT) method. The results showed that the BPD density could be effectively reduced by increasing the cooling rate, optimizing the seed-bonding method, and adopting a graphite crucible with a similar coefficient of thermal expansion as the SiC single crystal. The BPD density in the experiments showed that a high cooling rate reduced the BPD density from 4689 cm-2 to 2925 cm-2; optimization of the seed-bonding method decreased the BPD density to 1560 cm-2. The BPD density was further reduced to 704 cm-2 through the adoption of a graphite crucible with a smaller thermal expansion coefficient.

A Fast-Charge Graphite Anode with a Li-Ion-Conductive, Electron/Solvent-Repelling Interface.

Graphite has been serving as the key anode material of rechargeable Li-ion batteries, yet is difficultly charged within a quarter hour while maintaining stable electrochemistry. In addition to a defective edge structure that prevents fast Li-ion entry, the high-rate performance of graphite could be hampered by co-intercalation and parasitic reduction of solvent molecules at anode/electrolyte interface. Conventional surface modification by pitch-derived carbon barely isolates the solvent and electrons, and usually lead to inadequate rate capability to meet practical fast-charge requirements. Here we show that, by applying a MoOx-MoNx layer onto graphite surface, the interface allows fast Li-ion diffusion yet blocks solvent access and electron leakage. By regulating interfacial mass and charge transfer, the modified graphite anode delivers a reversible capacity of 340.3 mAh g-1 after 4000 cycles at 6 C, showing promises in building 10-min-rechargeable batteries with a long operation life.

Ni, Co, and Yb Cation Co-doping and Defect Engineering of FeOOH Nanorods as an Electrocatalyst for the Oxygen Evolution Reaction.

Electrocatalytic water splitting is a feasible technology that can produce hydrogen from renewable sources. The oxygen evolution reaction (OER), which has a slower kinetics and higher overpotential than the hydrogen evolution reaction, is the bottleneck that limits the overall water splitting. It is essential to develop efficient OER catalysts to reduce the anode overpotential. Herein, Ni,Co,Yb-FeOOH nanorod arrays grown directly on a carbon cloth are synthesized by a simple one-step hydrothermal method. The doped Ni2+ and Co2+ can occupy Fe2+ and Fe3+ sites in FeOOH, increasing the concentration of oxygen vacancies (VO), and the doped Yb3+ with a larger ionic radius can occupy the interstitial sites, which leads to more edge dislocations. VO and edge dislocations greatly enrich the active sites in FeOOH/CC. In addition, density functional theory calculations confirm that doping of Ni2+, Co2+, and Yb3+ modulates the electronic structure of the main active Fe sites, bringing its d-band center closer to the Fermi level and reducing the Gibbs free energy change of the rate-determining step of the OER. When the current density reaches 10 mA cm-2, the overpotential of Ni,Co,Yb-FeOOH/CC is only 230.9 mV, and the Tafel slope is 22.7 mV dec-1. In particular, a mechanism of multi-cation doping synergistic interaction with the oxygen vacancy and edge dislocation to enhance the OER catalytic activity of the material is proposed.

"Installation art"-like hierarchical self-assembly of giant polymeric elliptical platelets.

This paper reports the aqueous self-assembly of giant elliptical platelets over 20 µm in axial length, from a novel polyamide. Both the self-assembly pathway and mechanism were studied using morphology and X-ray characterizations. The polymer first self-organizes into small quadrangular frustum pyramid platelets, and then these small platelets can be further installed into giant elliptical platelets through an "installation art"-like hierarchical self-assembly process driven by crystallization. The as-prepared regular giant platelets can further aggregate together into multi-horned or flower-like superstructures.