Air-Stable Na3.5C6O6 as a Sodium Compensation Additive in Cathode of Na-Ion Batteries.

Sodium-ion battery (SIB) is a candidate for the stationary energy storage systems because of the low cost and high abundance of sodium. However, the energy density and lifespan of SIBs suffer severely from the irreversible consumption of the Na-ions for the formation of the solid electrolyte interphase (SEI) layer and other side reactions on the electrodes. Here, Na3.5C6O6 is proposed as an air-stable high-efficiency sacrificial additive in the cathode to compensate for the lost sodium. It is characteristic of low desodiation (oxidation) potential (3.4-3.6 V vs. Na+/Na) and high irreversible desodiation capacity (theoretically 378 mAh g-1). The feasibility of using Na3.5C6O6 as a sodium compensation additive is verified with the improved electrochemical performances of a Na2/3Ni1/3Mn1/3Ti1/3O2ǀǀhard carbon cells and cells using other cathode materials. In addition, the structure of Na3.5C6O6 and its desodiation path are also clarified on the basis of comprehensive physical characterizations and the density functional theory (DFT) calculations. This additive decomposes completely to supply abundant Na ions during the initial charge without leaving any electrochemically inert species in the cathode. Its decomposition product C6O6 enters the carbonate electrolyte without bringing any detectable negative effects. These findings open a new avenue for elevating the energy density and/or prolonging the lifetime of the high-energy-density secondary batteries.

Kinetic Limits of Graphite Anode for Fast-Charging Lithium-Ion Batteries.

Fast-charging lithium-ion batteries are highly required, especially in reducing the mileage anxiety of the widespread electric vehicles. One of the biggest bottlenecks lies in the sluggish kinetics of the Li+ intercalation into the graphite anode; slow intercalation will lead to lithium metal plating, severe side reactions, and safety concerns. The premise to solve these problems is to fully understand the reaction pathways and rate-determining steps of graphite during fast Li+ intercalation. Herein, we compare the Li+ diffusion through the graphite particle, interface, and electrode, uncover the structure of the lithiated graphite at high current densities, and correlate them with the reaction kinetics and electrochemical performances. It is found that the rate-determining steps are highly dependent on the particle size, interphase property, and electrode configuration. Insufficient Li+ diffusion leads to high polarization, incomplete intercalation, and the coexistence of several staging structures. Interfacial Li+ diffusion and electrode transportation are the main rate-determining steps if the particle size is less than 10 µm. The former is highly dependent on the electrolyte chemistry and can be enhanced by constructing a fluorinated interphase. Our findings enrich the understanding of the graphite structural evolution during rapid Li+ intercalation, decipher the bottleneck for the sluggish reaction kinetics, and provide strategic guidelines to boost the fast-charging performance of graphite anode.

Tunable Afterglow and Self-Trapped Exciton Emissions in Zr (IV)-Based Organic-Inorganic Metal Halide Hybrids by Metal-Ion Doping.

Low-dimensional hybrid metal halide (LDHMH) materials have attracted considerable attention owing to their intriguing optical properties. To the best of the knowledge, this is the first study to successfully demonstrate both self-trap exciton (STE) and afterglow emissions in Zr-based LDHMH materials. The obtained pure (Ph3 S)2 ZrCl6 crystals showed near-ultraviolet phosphorescence and a green afterglow owing to the organic cation Ph3 S+ , while the Bi-doped and Sb-doped crystals exhibited both STE and afterglow emissions. However, the Te-doped crystals showed only a broad yellow STE emission owing to the [TeCl6 ]2- octahedron. In addition, all the crystals showed good stability. Notably, Sb-doped crystals produced white light, which can be adjusted between cold white and warm white using different excitations. Finally, this strategy for both STE and afterglow emissions can be applied to other LDHMH materials for optical applications.

Multimodal Luminescent Low-Dimension Cs2ZrCl6:xSb3+ Crystals for White Light-Emitting Diodes and Information Encryption.

Low-dimension perovskite materials have attracted wide attention due to their excellent optical properties and stability. Herein, Sb3+-doped Cs2ZrCl6 crystals are synthesized by a coprecipitation method in which Sb3+ ions partially replace Zr4+ ions. The Cs2ZrCl6:xSb3+ powder shows blue and orange-red emissions under a 254 and 365 nm light, respectively, due to the [ZrCl6]2- octahedron and [SbCl6]3- octahedron. The photoluminescence quantum yield (PLQY) of Cs2ZrCl6:xSb3+ (x = 0.1) crystals is up to 52.5%. According to experimental and computational results, the emission mechanism of the Cs2ZrCl6:xSb3+ crystals is proposed. On the one hand, a wide blue emission with a large Stokes shift is caused by the self-trapping excitons of [ZrCl6]2- octahedra under a 260 nm excitation. On the other hand, the luminescence mechanism of [SbCl6]3- octahedron is divided into two parts: 1P1 → 1S0 (490 nm) and 3P1 → 1S0 (625 nm). The broad-band emission, high PLQY, and excellent stability endow the Cs2ZrCl6:xSb3+ powders with the potential for the fabrication of white light-emitting diodes (WLEDs). A WLED device is fabricated using a commercial 310 nm NUV chip, which shows a high color rendering index of 89.7 and a correlated color temperature of 5333 K. In addition, the synthesized Cs2ZrCl6:xSb3+ crystals can be also successfully used for information encryption. Our work will provide a deep understanding of the photophysical properties of Sb3+-doped perovskites and facilitate the development of Cs2ZrCl6:xSb3+ crystals in encrypting multilevel optical codes and WLEDs.

Achieving High-Efficiency Large-Area Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are semitransparent windows that are able to generate electricity from sunlight absorption. LSCs have shown huge promise for realizing building-integrated photovoltaics (BIPV). Unfortunately, to date, the power conversion efficiency (PCE) of LSCs is still very low which dramatically hampers their practical applications. In this Perspective, We summarize and review the latest developments of LSCs by looking at different structures. Among others, we focus more on the next developments in the field of LSCs, i.e., the possibility of high PCE, large area, mass production, and durability needed for future industrial development. We hope to promote the application of uniform testing standards and to draw attention to industrial development, toxicity, and durability. Then, we will provide a critical assessment of the field of LSCs. Finally, the challenge and solution will be discussed.

Achieving Ultrahigh Efficiency Vacancy-Ordered Double Perovskite Microcrystals via Ionic Liquids.

Lead-free perovskites have gained much interest for photovoltaic and optoelectronic applications. But instability and low quantum efficiency significantly limit their prospects for future applications. Here, a general route is reported to synthesize highly stable lead-free perovskites on a large scale with remarkably enhanced quantum efficiency. Two typical vacancy-ordered double perovskites (Cs2 ZrCl6 and Cs2 SnCl6 ) and their corresponding Bi3+ or Sb3+ doped samples are synthesized in ionic liquids (ILs) solutions via a simple solution method. These prepared perovskite samples all exhibit high-quality crystalline structures and their photoluminescence quantum yields (PLQYs) all show an increase close to 200% compared to the samples prepared in the hydrochloric acid system. The PLQY of Sb-doped Cs2 ZrCl6 with excellent thermal stability can reach up to 90.2%, which is the highest value reported for this system (Cs2 ZrCl6 :Sb). Density functional theory calculations reveal that the corresponding interaction between the ILs and the samples can effectively improve the crystal quality and reduce energy loss. The potential applications of the prepared samples for high-performance white light-emitting diodes and optical anti-counterfeiting are also demonstrated. The findings provide a straightforward way to obtain ultrahigh quantum efficiency vacancy-ordered double perovskites with good thermal stability and excellent optoelectronic properties.

Fast HCl-free Synthesis of Lead-free Rb2ZrCl6:xSb3+ Perovskites.

Due to the toxicity and instability issues of lead halide perovskites, lead-free perovskites have recently emerged as a viable alternative. However, significant optical band gaps of lead-free perovskites exert influence on their luminescent properties. Fortunately, the addition of dopants becomes an efficacious solution. The current widely utilized methods for synthesizing perovskites almost require high temperatures, a long period, and atmosphere protection, which cost more energy and resources. In this paper, we report that Rb2ZrCl6:xSb3+ perovskite phosphors can be easily prepared by a wet grinding approach at room temperature, which is a more efficient and facile process. Due to the self-trapped excitons of the host structure and Sb3+ ions, the produced samples display blue-white and orange fluorescence under UV lamp irradiation at 254 and 365 nm, respectively. In the photoluminescence spectrum, the doped perovskite exhibits an emission peak at 630 nm under excitation at 365 nm. Importantly, the prepared phosphors have tunable emissions related to the excitation wavelength. In addition, our produced powders show remarkable stability at room temperature, laying the foundations for this approach to be widely used in perovskite production.

Rapid and Large-Scale Preparation of Stable and Efficient White Light Emissive Perovskite Microcrystals Using Ionic Liquids.

In this work, we report large-scale preparation of stable Sb3+ and Bi3+ codoped Cs2ZrCl6 microcrystals for highly efficient white light emission using ionic liquids, demonstrating a broad dual-band white emission covering 400-800 nm. The dual emissions originate from the associated self-trapped excitons of the [SbCl6]3- and [BiCl6]3- octahedra. Moreover, the ratio of the dual-emission peaks can be effectively regulated by tuning the excitation wavelength. Meanwhile, to improve the optical properties and stability, ionic liquids are employed to assist the synthesis process of perovskite materials. The white light emission of one of the samples demonstrates CIE coordinates right in the center of the white light region (0.334, 0.331) and an excellent color rendering index (∼90.3), accompanied by a 66.1% quantum efficiency. Moreover, our method allows the facile synthesis of large batches of microcrystalline powders. Our findings demonstrate the potential of white phosphors as single components for future applications in lighting fields.

Ionic Liquid-Assisted Fast Synthesis of Carbon Dots with Strong Fluorescence and Their Tunable Multicolor Emission.

Conventional synthesis of carbon dots (CDs) mostly involves a hydrothermal or solvent-thermal reaction which needs relatively high temperature and pressure. In this work, ionic liquid is used to assist in fast synthesizing CDs with an ultrahigh photoluminescent quantum yield (98.5%) by heating at a low temperature (≤100 °C) and at atmospheric pressure. In addition, through this approach, tunable multicolor emissive CDs can be successfully achieved and used for preparing high-performance white light-emitting diodes. Theoretical computation proves that the activity of synthesis reaction can be significantly enhanced by ionic liquids. Density functional theory calculation reveals that the size and graphite nitrogen ratios of CDs have an effect on bandgap reduction, resulting in a redshift of the emission, which is in good agreement with the experimental results. This simple and promising approach for fast synthesis of tunable emissive CDs using ionic liquid affords the facilitation of CDs-based luminescent materials for fast manufacturing of functional devices.

Carbon dots and AIE molecules for highly efficient tandem luminescent solar concentrators.

We used N-doped carbon dots and TPFE-Rho aggregation-induced emission (AIE) fluorescent materials to fabricate tandem luminescent solar concentrators. The fluorescence quantum yields of N-CDs and TPFE-Rho are 79.65% and 34.88%, respectively. High-performance tandem LSCs can be obtained.