The rapidly developing market for mobile electronics and hybrid electric vehicles (HEVs) has prompted the urgent need for batteries with high energy density, long cycle life, high efficiency, and low cost.[1] Recently, rechargeable lithium-sulfur (Li-S) batteries have attracted considerable attention because of their high theoretical gravimetric (volumetric) energy density of 2570 W h kg À1 (2200 W h l À1 ), and low cost. [2] However, the use of S as cathode material for Li-S batteries suffers from two major issues. One is the insulating nature of S, which results in low active-material utilization and limited rate capability.[2a] The other is the formation of electrolytesoluble polysulfides; these polysulfide intermediates, which are generated in the discharge/charge process, dissolve in the electrolyte and migrate to the Li anode, a process known as the shuttle effect.[3] Consequently, the S cathode suffers a significant loss of S during cycling, resulting in a rapid capacity decrease. Many strategies have been used to address these problems, such as the impregnation of S into various conductive porous matrixes, [4] surface coating of S, [5] and the use of suitable electrolytes [6] and additives. [7] Although remarkable improvements have been achieved, the application of Li-S batteries is still hindered by the intrinsic drawbacks of S. Therefore, it is of great importance to explore and develop new high-energy cathode materials with improved electronic conductivity and cycling stability, to cover the shortfalls of S and provide alternative choices for practical applications.From this perspective, selenium, an element belonging to the same group in the periodic table as sulfur, is a prospective candidate for cathode materials. Although Se has a lower theoretical gravimetric capacity (675 mA h g À1 ) than S (1675 mA h g À1 ), its higher density (ca. 2.5 times that of S) offsets the deficiency and provides a high theoretical volumetric capacity density (3253 mA h cm À3 ), comparable to that of S (3467 mA h cm À3 ). It has been reported that Li-Se batteries deliver a high output voltage, [8] so Li-Se batteries are also expected to have a high volumetric energy density. It is known that for applications in portable devices and HEVs, volumetric energy density is more important than gravimetric energy density because of the limited battery packing space. [9] Moreover, the electronic conductivity of Se (1 10 À3 S m À1 ) is considerably higher than that of S (5 10 À28 S m À1 ), [8] which suggests that Se could have higher utilization rate, better electrochemical activity, and faster electrochemical reaction with Li. Therefore, the advantages of Se promise an attractive alternative cathode material for building high-energy batteries for specific applications, including consumer electronics and transportation. However, at present, research on Li-Se batteries is still at a very early stage.Recently, Abouimrane et al. [8] conducted pioneering work on the use of Se as a cathode material. The results show that, even bulk ...

The Li metal anode has long been considered as one of the most ideal anodes due to its high energy density. However, safety concerns, low efficiency, and huge volume change are severe hurdles to the practical application of Li metal anodes, especially in the case of high areal capacity. Here it is shown that that graphitized carbon fibers (GCF) electrode can serve as a multifunctional 3D current collector to enhance the Li storage capacity. The GCF electrode can store a huge amount of Li via intercalation and electrodeposition reactions. The as-obtained anode can deliver an areal capacity as high as 8 mA h cm and exhibits no obvious dendritic formation. In addition, the enlarged surface area and porous framework of the GCF electrode result in lower local current density and mitigate high volume change during cycling. Thus, the Li composite anode displays low voltage hysteresis, high plating/stripping efficiency, and long lifespan. The multifunctional 3D current collector promisingly provides a new strategy for promoting the cycling lifespan of high areal capacity Li anodes.

Lithium metal is a promising battery anode. However, inhomogeneous mass and charge transfers across the Li/electrolyte interface result in formation of dendritic Li and "dead" Li, and an unstable solid electrolyte interphase, which incur serious problems to impede its service in rechargeable batteries. Here, we show that the above problems can be mitigated by regulating the interfacial mass/charge transfer. The key to our strategy is hybrid Li storage in onion-like, graphitized spherical C granules wired on a three-dimensional conducting skeleton, which enhances the negativity of surface charge of the C host to contribute to a uniform Li plating while also forming stable Li/C intercalation compounds to offset any irreversible Li loss during cycling. As a result, the anode shows a suppressed dendrite formation and a high Li utilization >95%, enabling a practical Li battery to strike a long lifespan of 1000 cycles at a surplus Li of merely 5%.

Lithium metal has been deemed the most attractive anode for high-energy-density batteries due to its high theoretical capacity and low anode potential. Unfortunately, its development still faces various challenges, mainly including dendritic Li growth and low Coulombic efficiency. Here, we constructed a flexible and free-standing 3D hollow carbon fiber container with porous skeleton, which can suppress Li dendrite growth and bring about high Coulombic efficiency, large areal capacity, long lifespan, and good full cell performance.

To exploit the high energy density of lithium-sulfur batteries, porous carbon materials have been widely used as the host materials of the S cathode. Current studies about carbon hosts are more frequently focused on the design of carbon structures rather than modification of its properties. In this study, we use boron-doped porous carbon materials as the host material of the S cathode to get an insightful investigation of the effect of B dopant on the S/C cathode. Powder electronic conductivity shows that the B-doped carbon materials exhibit higher conductivity than the pure analogous porous carbon. Moreover, by X-ray photoelectron spectroscopy, we prove that doping with B leads to a positively polarized surface of carbon substrates and allows chemisorption of S and its polysulfides. Thus, the B-doped carbons can ensure a more stable S/C cathode with satisfactory conductivity, which is demonstrated by the electrochemical performance evaluation. The S/B-doped carbon cathode was found to deliver much higher initial capacity (1300 mA h g(-1) at 0.25 C), improved cyclic stability, and rate capability when compared with the cathode based on pure porous carbon. Electrochemical impedance spectra also indicate the low resistance of the S/B-doped C cathode and the chemisorption of polysulfide anions because of the presence of B. These features of B doping can play the positive role in the electrochemical performance of S cathodes and help to build better Li-S batteries.

choices for the next-generation energy storage devices because of their surpassed energy output. [3] However, the inherent defects of Li anode incur serious problems that restrict the utilization of rechargeable Li metal batteries. [4] First, an uneven plating/stripping of Li leads to the formation and growth of Li dendrites. The formed Li dendrites may puncture the separator and induce internal short circuit, bring severe safety concerns. Second, Li has a relatively high Fermi energy and thus easily reacts with the liquid electrolyte to form an unstable solid-electrolyte interphase (SEI) on the anode surface. The persistent reaction between Li metal and electrolyte consumes both of them, and results in a low Coulombic efficiency and rapid capacity fade of anode. Third, the plating of Li is actually a "hostless" process. Therefore, the relative change of volume for Li metal anode is virtually infinite, which may induce immense internal stress fluctuation of battery and account for seriously deteriorated performance.Great efforts have been devoted to addressing the above problems of Li anode. A number of works focus on optimizing the electrolyte components and additives to homogenize the Li + flux for plating and improve the stability and uniformity of the SEI on the anode surface. [5] However, the resultant SEI layer has been revealed not sufficiently sturdy to accommodate the morphological change of the Li anode surface, and can be broken down upon repeated Li plating/stripping. [6] Therefore, solid electrolytes and various mechanical barriers with high shear modulus have been explored to suppress dendrite formation. [7] Given the simple physical blocking function of the mechanical barrier, these strategies do not alter the fundamental chemical/ electrochemical properties of Li and thereby show a limited dendrite-proof effect. Furthermore, most solid electrolytes show low ionic conductivity and critical interfacial issues in their contacts with both electrodes. Recently, the development of a threedimensional (3D) porous current collector has been considered as a feasible route to prohibit the growth of Li dendrite. [8] The 3D interconnected architectures provide a large specific surface area, enabling low current density and uniform distribution of the positive charges, while the porous structure ensures ample space to accommodate Li, limiting the growth of Li dendrite and alleviating the huge volume change of Li metal during cycling. For example, 3D porous copper current collector consisting of a large number of protuberant tips has been regarded Metallic lithium is considered as a competitive anode candidate for rechargeable Li batteries due to its ultrahigh theoretical specific capacity of 3860 mA h g −1 . However, hurdles regarding the uneven Li deposition, unstable solid electrolyte interphase formation, and infinite change of relative dimensions challenge its practical application. Porous carbons (PCs), due to their high conductivity and stable electrochemistry, have been demonstrated feasible as ho...

As a crucial component, carbon substrates with appropriate porous structures are highly desired in developing sulfur-carbon cathodes for Li-S batteries with superior performance. Here we show that the electrochemical performance of the sulfur-carbon cathode can be easily adjusted by tuning the pore structure of the carbon substrate. With potassium hydroxide as the activation agent, a series of micro-/ mesoporous carbon hosts have been prepared via chemical activation of hydrothermal carbon precursors. The pore structure of the carbon host can be easily controlled by adjusting the activation concentration of KOH, and is found to be directly related to the battery performance of sulfur loaded inside. An optimized pore structure is yielded at a KOH concentration of 1 M, at which the sulfurcarbon cathode shows a high specific capacity, favourable rate capabilities and a long cycle life of 800 cycles at 1 C. The impressive electrochemical performances benefit from the advanced micro-/ mesoporous carbon spheres with a large percentage of micropores, moderate activation and surface area.

Reactive oxygen species (ROS) play crucial roles in biological metabolism and intercellular signaling. However, ROS level is dramatically elevated due to abnormal metabolism during multiple pathologies, including neurodegenerative diseases, diabetes, cancer, and premature aging. By taking advantage of the discrepancy of ROS levels between normal and diseased tissues, a variety of ROS-sensitive moieties or linkers have been developed to design ROS-responsive systems for the site-specific delivery of drugs and genes. In this review, we summarized the ROS-responsive chemical structures, mechanisms, and delivery systems, focusing on their current advances for precise drug/gene delivery. In particular, ROS-responsive nanocarriers, prodrugs, and supramolecular hydrogels are summarized in terms of their application for drug/gene delivery, and common strategies to elevate or diminish cellular ROS concentrations, as well as the recent development of ROS-related imaging probes were also discussed.