Lithium-sulfur (Li-S) batteries are severely hindered by the low sulfur utilization and short cycling life, especially at high rates. One of the effective solutions to address these problems is to improve the sulfiphilicity of lithium polysulfides (LiPSs) and the lithiophilicity of the lithium anode. However, it is a great challenge to simultaneously optimize both aspects. Herein, by incorporating the merits of strong absorbability and high conductivity of SnS with good catalytic capability of ZnS, a ZnS-SnS heterojunction coated with a polydopamine-derived N-doped carbon shell (denoted as ZnS-SnS@NC) with uniform cubic morphology was obtained and compared with the ZnS-SnS@NC heterostructure and its single-component counterparts (SnS@NC and SnS@NC). Theoretical calculations, XANES, and Raman spectrum were utilized to elucidate rapid anchoring-diffusion-transformation of LiPSs, inhibition of the shuttling effect, and improvement of the sulfur electrochemistry of bimetal ZnS-SnS heterostructure at the molecular level. When applied as a modification layer coated on the separator, the ZnS-SnS@NC-based cell with optimized lithiophilicity and sulfiphilicity enables desirable sulfur electrochemistry, including high reversibility of 1149 mAh g for 300 cycles at 0.2 C, high rate performance of 661 mAh g at 10 C, and long cycle life with a low fading rate of 0.0126% each cycle after 2000 cycles at 4 C. Furthermore, a favorable areal capacity of 8.27 mAh cm is maintained under high sulfur mass loading of 10.3 mg cm. This work furnishes a feasible scheme to the rational design of bimetal sulfides heterostructures and boosts the development of other electrochemical applications.

The goal of replacing combustion engines or reducing their use presents a daunting problem for society. Current lithium-ion technologies provide a stepping stone for this dramatic but inevitable change. However, the theoretical gravimetric capacity (∼300 mA h g(-1)) is too low to overcome the problems of limited range in electric vehicles, and their cost is too high to sustain the commercial viability of electrified transportation. Sulfur is the one of the most promising next generation cathode materials. Since the 1960s, researchers have studied sulfur as a cathode, but only recently have great strides been made in preparing viable composites that can be used commercially. Sulfur batteries implement inexpensive, earth-abundant elements at the cathode while offering up to a five-fold increase in energy density compared with present Li-ion batteries. Over the past few years, researchers have come closer to solving the challenges associated with the sulfur cathode. Using carbon or conducting polymers, researchers have wired up sulfur, an excellent insulator, successfully. These conductive hosts also function to encapsulate the active sulfur mass upon reduction/oxidation when highly soluble lithium polysulfides are formed. These soluble discharge products remain a crux of the Li-S cell and need to be contained in order to increase cycle life and capacity retention. The use of mesoporous carbons and tailored designs featuring porous carbon hollow spheres have led to highly stable discharge capacities greater than 900 mA h g(-1) over 100 cycles. In an attempt to fully limit polysulfide dissolution, methods that rely on coating carbon/sulfur composites with polymers have led to surprisingly stable capacities (∼90% of initial capacity retained). Additives will also play an important role in sulfur electrode design. For example, small fractions (> 3 wt%) of porous silica or titania effectively act as polysulfide reservoirs, decreasing their concentration in the electrolyte and leading to a higher utilization of sulfur and increased capacities.

Due to the high theoretical energy density of 2600 Wh kg(-1), lithium-sulfur batteries are strongly regarded as the promising next-generation energy storage devices. However, the practical applications of lithium-sulfur batteries are challenged by several obstacles, including the low sulfur utilization and poor lifespan, which are partly attributed to the shuttle of lithium polysulfides and lithium dendrite growth in working lithium-sulfur batteries. Suppressing lithium dendrite growth is a necessary step not only for a safe and efficient Li metal anode, but also for a high capacity cell with a high Coulombic efficiency. Herein we review the lithium metal anode protection in a polysulfide-rich environment, relative to most reviews on lithium metal anode without considering the effect of lithium polysulfides in lithium metal batteries. Firstly, the importance and dilemma of Li metal anode issues in lithium-sulfur batteries are underscored, aiming to arouse the attentions to Li metal anode protection. Specific attentions are paid to the surface chemistry of Li metal anode in a polysulfide-rich lithium-sulfur battery. Next, the proposed strategies to stabilize solid electrolyte interface and protect Li metal anode are included. Finally, a general conclusion and a perspective on the current limitations, as well as recommended future research directions of Li metal anode in lithium-sulfur batteries are presented. (C) The Author(s) 2017. Published by ECS.

With the progress of science and the development of human society, traditional energy is increasingly exhausted, and low energy density lithium ion battery is not enough to support the demand for energy, so the development of high capacity of clean energy system is imminent. Unlike Li-ion batteries, Li-sulfur batteries have a high specific energy density (2600 Wh•kg−1), making them a promising energy storage system. However, in oxidation-reduction reaction, the shuttle effect of intermediate polysulfides (LiPSs) and slow electrochemical reaction kinetics lead to severe degradation of the cathode and anode, resulting in rapid capacity decay. In this paper, a multifunctional FeP/carbon cloth (FeP/CC) interlayer was prepared by hydrothermal synthesis. The FeP grows evenly in a “needle” shape on a smooth carbon cloth. This structure provides more active sites for Li-S batteries and greatly improves the electrochemical reaction kinetics by utilizing the catalytic ability of phosphate to Li-S batteries. In addition, carbon cloth (CC), as the matrix, can also play the role of “physical domain limiting”, thereby physically trapping LiPSs, inhibiting the shuttle effect and ensuring the cycle stability. In subsequent electrochemical tests, the FeP/CC interlayer lithium-sulfur battery had a first cycle discharge capacity of 1329 mAh•g−1 and a reversible capacity of 1100 mAh•g−1 after 100 cycles. When the sulfur load reaches 3.4 mg•cm−2 and the current density is 1 C, the cyclic capacity is stable at 495 mAh•g−1. In addition, FeP/CC showed excellent adsorption and catalytic conversion ability for LiPSs in visual adsorption experiments and ultraviolet spectrum tests. This multifunctional FeP/CC interlayer provides a feasible idea for the development of high stability and high capacity lithium-sulfur batteries.

Li-S batteries (LSBs) require a minimum 6 mAh cm areal capacity to compete with the state-of-the-art lithium ion batteries (LIBs). However, this areal capacity is difficult to achieve due to a major technical issue-the shuttle effect. Nonpolar carbon materials limit the shuttle effect through physical confinement. However, the polar polysulfides (PSs) only provide weak intermolecular interactions (0.1-0.7 eV) with these nonpolar carbon materials. The physically encapsulated PSs inside the nonpolar carbon scaffold eventually diffuses out and starts shuttling. Chemically interactive hosts are more effective at interacting with the PSs due to high binding energies. Herein, a multifunctional separator coating of nitrogen-doped multilayer graphene (NGN) and -SO containing Nafion (N-NGN) is used to mitigate PS shuttling and to produce a high areal capacity LSB. The Nafion is used as a binder instead of PVDF to provide an additional advantage of -SO to chemically bind the PS. The motive of this research is to investigate the effect of highly electronegative N and -SO (N-NGN) in comparison with the -OH, -COOH, and -SO groups from a hydroxyl graphene and Nafion composite (N-OHGN) to mitigate PS shuttling in LSBs. The highly conductive doped graphene architecture (N-NGN) provides efficient pathways for both electrons and ions, which accelerates the electrochemical conversion at high sulfur loading. Moreover, the electron-rich pyridine N and -SO show strong chemical affinity with the PS through polar-polar interactions, which is proven by the superior electrochemical performance and density functional theory calculations. Further, the N-NGN (5 h) produces a maximum areal capacity of 12.0 and 11.0 mAh cm, respectively, at 15 and 12 mg cm sulfur loading. This areal capacity limit is significantly higher than the required areal capacity of LSBs for commercial application, which shows the significant strength of N-NGN as an excellent separator coating for LSBs.Copyright © 2019 American Chemical Society.

Ceramic biomaterials have been investigated for several decades, but their potential biomedical applications in cancer therapy have been paid much less attentions, mainly due to their lack of related material functionality for combating the cancer. In this work, we report, for the first time, that MAX ceramic biomaterials exhibit the unique functionality for the photothermal ablation of cancer upon being exfoliated into ultrathin nanosheets within atomic thickness (MXene). As a paradigm, biocompatible TiC nanosheets (MXenes) were successfully synthesized based on a two-step exfoliation strategy of MAX phase TiAlC by the combined HF etching and TPAOH intercalation. Especially, the high photothermal-conversion efficiency and in vitro/in vivo photothermal ablation of tumor of TiC nanosheets (MXenes) were revealed and demonstrated, not only in the intravenous administration of soybean phospholipid modified TiC nanosheets but also in the localized intratumoral implantation of a phase-changeable PLGA/TiC organic-inorganic hybrid. This work promises the great potential of TiC nanosheets (MXenes) as a novel ceramic photothermal agent used for cancer therapy and may arouse much interest in exploring MXene-based ceramic biomaterials to benefit the biomedical applications.

Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.Copyright © 2016, American Association for the Advancement of Science.