Because of its unprecedented theoretical capacity near 4000 mAh/g, which is approximately 10-fold larger compared to those of the current commercial graphite anodes, silicon has been the most promising anode for lithium ion batteries, particularly targeting large-scale energy storage applications including electrical vehicles and utility grids. Nevertheless, Si suffers from its short cycle life as well as the limitation for scalable electrode fabrication. Herein, we develop an electrospinning process to produce core-shell fiber electrodes using a dual nozzle in a scalable manner. In the core-shell fibers, commercially available nanoparticles in the core are wrapped by the carbon shell. The unique core-shell structure resolves various issues of Si anode operations, such as pulverization, vulnerable contacts between Si and carbon conductors, and an unstable sold-electrolyte interphase, thereby exhibiting outstanding cell performance: a gravimetric capacity as high as 1384 mAh/g, a 5 min discharging rate capability while retaining 721 mAh/g, and cycle life of 300 cycles with almost no capacity loss. The electrospun core-shell one-dimensional fibers suggest a new design principle for robust and scalable lithium battery electrodes suffering from volume expansion.

Na-S batteries are one type of molten salt battery and have been used to support stationary energy storage systems for several decades. Despite their successful applications based on long cycle lives and low cost of raw materials, Na-S cells require high temperatures above 300 °C for their operations, limiting their propagation into a wide range of applications. Herein, we demonstrate that Na-S cells with solid state active materials can perform well even at room temperature when sulfur-containing carbon composites generated from a simple thermal reaction were used as sulfur positive electrodes. Furthermore, this structure turned out to be robust during repeated (de)sodiation for ~500 cycles and enabled extraordinarily high rate performance when one-dimensional morphology is adopted using scalable electrospinning processes. The current study suggests that solid-state Na-S cells with appropriate atomic configurations of sulfur active materials could cover diverse battery applications where cost of raw materials is critical.

A covalent triazine framework (CTF) with embedded polymeric sulfur and a high sulfur content of 62 wt % was synthesized under catalyst- and solvent-free reaction conditions from 1,4-dicyanobenzene and elemental sulfur. Our synthetic approach introduces a new way of preparing CTFs under environmentally benign conditions by the direct utilization of elemental sulfur. The homogeneous sulfur distribution is due to the in situ formation of the framework structure, and chemical sulfur impregnation within the micropores of CTF effectively suppresses the dissolution of polysulfides into the electrolyte. Furthermore, the triazine framework facilitates electron and ion transport, which leads to a high-performance lithium-sulfur battery.

5359 www.MaterialsViews.com wileyonlinelibrary.com density, which is approximately 6.6 times larger than that of the current intercalationbased LIBs (≈387 Wh kg −1 ). [5][6][7][8] Remarkably, recent research efforts have been successful in resolving the chronic technical challenges associated with sulfur electrodes, especially dissolution of lithium polysulfi des and low electric conductivity of elemental sulfur. [9][10][11][12] The representative solutions along this direction include sulfur-carbon composite structures that minimize sulfur exposure to electrolyte, [ 5,13 ] surface coating of active particles, [ 7,[14][15][16] engagement of allotropic sulfur, [ 17,18 ] and use of solid-state electrolytes [ 19 ] and electrolyte additives. [ 20,21 ] Although the improved cycle lives based on these approaches represent considerable progresses in the area of Li-S batteries, it should be noted that the most critical issue related to Li metal anodes still remains unaddressed: upon repeated charge and discharge, Li dendrites grow on the surface of the Li metal anode, which triggers multiple mechanisms for rapid capacity fading. The electrolyte becomes decomposed successively along the Li dendrite surfaces, which destabilizes the electrode-electrolyte interface and also increases the resistance (or overpotential) leading to continuous capacity decay. The electrolyte could be eventually exhausted. The dendrite growth could also promote short circuits between both electrodes, and thus resulting in severe safety hazard. [ 22 ] An additional but very critical hurdle related to the Li dendrite growth is that the dendrite growth becomes accelerated with areal current density. [22][23][24][25][26] Hence, the increase in the areal capacity of sulfur electrode (or the areal mass loading of sulfur active material) would amplify the problems originating from Li dendrites. Likewise, the dissolution of the fatal lithium polysulfi des would also be amplifi ed under the increased areal capacity. The demonstration of improved cycle lives from most of recent sulfur electrode designs, in turn, implies that the cycling tests were conducted with moderate mass loadings of the sulfur active materials. Therefore, in order to exalt Li-S batteries to more practical technology, more systematic approaches need to be engaged to resolve the issues from both sides of electrodes.With purpose of developing Li-S cells with high areal energy densities, herein, we have adopted or discovered the key cell components (sulfur electrode, separator, and electrolyte) in a way that Li dendrite formation and polysulfi de dissolution are minimized even at a practically viable loading of sulfur active material (≈17 mg cm −2 , the mass of sulfur-carbon composite). The synergistic outcomes from smart engineering of eachThe battery community has recently witnessed a considerable progress in the cycle lives of lithium-sulfur (Li-S) batteries, mostly by developing the electrode structures that mitigate fatal dissolution of lithium polysulfi des. Nonetheless, most of the ...

Nanostructured silicon electrodes have shown great potential as lithium ion battery anodes because they can address capacity fading mechanisms originating from large volume changes of silicon alloys while delivering extraordinarily large gravimetric capacities. Nonetheless, synthesis of well-defined silicon nanostructures in an industrially adaptable scale still remains as a challenge. Herein, we adopt an industrially established spray drying process to enable scalable synthesis of silicon-carbon composite particles in which silicon nanoparticles are embedded in porous carbon particles. The void space existing in the porous carbon accommodates the volume expansion of silicon and thus addresses the chronic fading mechanisms of silicon anodes. The composite electrodes exhibit excellent electrochemical performance, such as 1956 mAh/g at 0.05C rate and 91% capacity retention after 150 cycles. Moreover, the spray drying method requires only 2 s for the formation of each particle and allows a production capability of ~10 g/h even with an ultrasonic-based lab-scale equipment. This investigation suggests that established industrial processes could be adaptable to the production of battery active materials that require sophisticated nanostructures as well as large quantity syntheses.