Dual redox mediators accelerate the electrochemical kinetics of lithium-sulfur batteries.

The sluggish electrochemical kinetics of sulfur species has impeded the wide adoption of lithium-sulfur battery, which is one of the most promising candidates for next-generation energy storage system. Here, we present the electronic and geometric structures of all possible sulfur species and construct an electronic energy diagram to unveil their reaction pathways in batteries, as well as the molecular origin of their sluggish kinetics. By decoupling the contradictory requirements of accelerating charging and discharging processes, we select two pseudocapacitive oxides as electron-ion source and drain to enable the efficient transport of electron/Li+ to and from sulfur intermediates respectively. After incorporating dual oxides, the electrochemical kinetics of sulfur cathode is significantly accelerated. This strategy, which couples a fast-electrochemical reaction with a spontaneous chemical reaction to bypass a slow-electrochemical reaction pathway, offers a solution to accelerate an electrochemical reaction, providing new perspectives for the development of high-energy battery systems.

Class of Solid-like Electrolytes for Rechargeable Batteries Based on Metal-Organic Frameworks Infiltrated with Liquid Electrolytes.

A new family of solid-like electrolytes was developed by infiltrating MIL-100(Al), an electrochemically stable metal-organic-framework (MOF) material, with liquid electrolytes that contain cations from the 3rd period (Na+, Mg2+, and Al3+) and the 1st group (Li+, Na+, K+, and Cs+). The anions were immobilized within the MOF scaffolds upon complexing with the open metal sites, allowing effective transport of the cations in the nanoporous channels with high conductivity (up to 1 mS cm-1) and low activation energy (down to 0.2 eV). This general approach enables the fabrication of superior conductive solid-like electrolytes beyond lithium ions.

Covalently Bonded Si-Polymer Nanocomposites Enabled by Mechanochemical Synthesis as Durable Anode Materials.

Silicon is one of the most promising anode materials for lithium-ion batteries due to its high theoretical capacity and low cost. However, significant capacity fading caused by severe structural degradation during cycling limits its practical implication. To overcome this barrier, we design a covalently bonded nanocomposite of silicon and poly(vinyl alcohol) (Si-PVA) by high-energy ball-milling of a mixture of micron-sized Si and PVA. The obtained Si nanoparticles are wrapped by resilient PVA coatings that covalently bond to the Si particles. In such nanostructures, the soft PVA coatings can accommodate the volume change of the Si particles during repeated lithiation and delithiation. Simultaneously, as formed covalent bonds enhance the mechanical strength of the coatings. Due to the significantly improved structural stability, the Si-PVA composite delivers a lifespan of 100 cycles with a high capacity of 1526 mAh g-1. In addition, a high initial Coulombic efficiency of over 86% and an average value of 99.2% in subsequent cycles can be achieved. This reactive ball-milling strategy provides a low-cost and scalable route to fabricate high-performance anode materials.

Electrolyte Membranes with Biomimetic Lithium-Ion Channels.

High-performance lithium-ion batteries (LIBs) demand efficient and selective transport of lithium ions. Inspired by ion channels in biology systems, lithium-ion channels are constructed by chemically modifying the nanoporous channels of metal-organic frameworks (MOFs) with negatively charged sulfonate groups. Analogous to the biological ion channels, such pendant anionic moieties repel free anions while allowing efficient transport of cations through the pore channels. Implementing such MOFs as an electrolyte membrane doubly enhances the lithium-ion transference number, alleviates concentration polarization, and affords striking durability of high-rate LIBs. This work demonstrates an ion-selective material design that effectively tunes the ion-transport behavior and could assist with more efficient operation of LIBs.

CVD-assisted fabrication of hierarchical microparticulate Li2TiSiO5-carbon nanospheres for ultrafast lithium storage.

Particular recent interest has been given to the Li2TiSiO5 (LTSO) anode material owing to its low lithiation potential (0.28 V vs. Li/Li+) and decent theoretical capacity (308 mA h g-1). However, its poor electronic conductivity (∼10-7 S m-1) fundamentally limits the utilization of this material, and current strategies fail to tackle such issues in practical ways. Herein, a hierarchical microparticulate LTSO-carbon composite (LTSO/C) is fabricated by chemical vapor deposition (CVD), where microsized LTSO/C particles assembled from nanospheres guarantee a practical tap density of ∼1.3 g mL-1. Meanwhile, significantly elevated conductivity of LTSO/C (∼103 S m-1) is achieved by a thin layer (15 nm) of graphitic carbon growth on LTSO, which is theoretically catalyzed by the surface functional groups on the parent LTSO. The electrochemical characterization of LTSO/C reveals a superior graphite-like volumetric capacity of 441.1 mA h cm-3 and Li4Ti5O12-like rate capability (120.1 mA h cm-3 at 4.5 A g-1), providing inspiring guidance for designing analogous Ti or Si-based compounds for ultrafast lithium storage materials.

Rapid and Wide-Range Detection of NOx Gas by N-Hyperdoped Silicon with the Assistance of a Photovoltaic Self-Powered Sensing Mode.

Wide-dynamic-range NOx sensors are vital for the environment and health purposes, but few sensors could achieve wide-range detection with ultralow and ultrahigh concentrations at the same time. In this article, the microstructured and nitrogen-hyperdoped silicon (N-Si) for NOx gas sensing is investigated systematically. Working by the change of surface conductivity, the sensor is ultrasensitive to low concentrations of NOx down to 11 ppb and shows a rapid response/recovery time of 22/33 s for 80 ppb. When the NOx concentration increases and exceeds a threshold value (10-50 ppm), an n-p conduction-type transition is observed due to the inversion of the conduction type of major carriers, which limits the dynamic range of the sensor at high concentration. However, when the sensor works in a photovoltaic self-powered mode under the asymmetric light illumination, the limitation can be successfully overcome. Therefore, with the combination of the two working principles, a wide dynamic range stretching over 6 orders of magnitude (∼0.011-4000 ppm) can be achieved.

Anion-Sorbent Composite Separators for High-Rate Lithium-Ion Batteries.

Novel composite separators containing metal-organic-framework (MOF) particles and poly(vinyl alcohol) are fabricated by the electrospinning process. The MOF particles containing opened metal sites can spontaneously adsorb anions while allowing effective transport of lithium ions in the electrolyte, leading to dramatically improved lithium-ion transference number tLi + (up to 0.79) and lithium-ion conductivity. Meanwhile, the incorporation of the MOF particles alleviates the decomposition of the electrolyte, enhances the electrode reaction kinetics, and reduces the interface resistance between the electrolyte and the electrodes. Implementation of such composite separators in conventional lithium-ion batteries leads to significantly improved rate capability and cycling durability, offering a new prospective toward high-performance lithium-ion batteries.

"Infinite Sensitivity" of Black Silicon Ammonia Sensor Achieved by Optical and Electric Dual Drives.

The microstructured and hyperdoped silicon as a superior photoelectric and photovoltaic material is first studied as a gas-sensing material. The material is prepared by femtosecond-laser irradiation on selenium-coated silicon and then fabricated as a conductive gas sensor, targeting ammonia. At room temperature, the sensitivity, response time, repeatability, distinguishability, selectivity, and natural aging effect of the sensor have been systematically studied. Results show that such black silicon has good potential for application as an ammonia-sensing material. On the basis of its unique optoelectronic properties, an additional optical drive is proposed for the formation of an optical and electric dual-driven sensor, which is achieved by asymmetric light illumination between the two electrode regions. In a certain range of applied voltage, the sensitivity is enhanced dramatically and even tends to be infinite. For the aged device with degraded sensitivity, a two-order increment is obtained for 500 ppm of NH3 under the extra optical drive. A mechanism based on Dember effect is proposed for explaining such a phenomenon.