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.

Wearable electronics represent a significant paradigm shift in consumer electronics since they eliminate the necessity for separate carriage of devices. In particular, integration of flexible electronic devices with clothes, glasses, watches, and skin will bring new opportunities beyond what can be imagined by current inflexible counterparts. Although considerable progresses have been seen for wearable electronics, lithium rechargeable batteries, the power sources of the devices, do not keep pace with such progresses due to tenuous mechanical stabilities, causing them to remain as the limiting elements in the entire technology. Herein, we revisit the key components of the battery (current collector, binder, and separator) and replace them with the materials that support robust mechanical endurance of the battery. The final full-cells in the forms of clothes and watchstraps exhibited comparable electrochemical performance to those of conventional metal foil-based cells even under severe folding-unfolding motions simulating actual wearing conditions. Furthermore, the wearable textile battery was integrated with flexible and lightweight solar cells on the battery pouch to enable convenient solar-charging capabilities.

Considering the promising electrochemical performance of the recently reported pyrophosphate family in lithium ion batteries as well as the increasing importance of sodium ion batteries (SIBs) for emerging large‐scale applications, here, the crystal structure, electrochemical properties, and thermal stability of Na2FeP2O7, the first example ever reported in the pyrophosphate family for SIBs, are investigated. Na2FeP2O7 maintains well‐defined channel structures (triclinic framework under the P1 space group) and exhibits a reversible capacity of ≈90 mAh g−1 with good cycling performance. Both quasi‐equilibrium measurements and first‐principles calculations consistently indicate that Na2FeP2O7 undergoes two kinds of reactions over the entire voltage range of 2.0–4.5 V (vs Na/Na+): a single‐phase reaction around 2.5 V and a series of two‐phase reactions in the voltage range of 3.0–3.25 V. Na2FeP2O7 shows excellent thermal stability up to 500 °C, even in the partially desodiated state (NaFeP2O7), which suggests its safe character, a property that is very critical for large‐scale battery applications.

Spinel-structured lithium manganese oxide (LiMn(2)O(4)) cathodes have been successfully commercialized for various lithium battery applications and are among the strongest candidates for emerging large-scale applications. Despite its various advantages including high power capability, however, LiMn(2)O(4) chronically suffers from limited cycle life, originating from well-known Mn dissolution. An ironical feature with the Mn dissolution is that the surface orientations supporting Li diffusion and thus the power performance are especially vulnerable to the Mn dissolution, making both high power and long lifetime very difficult to achieve simultaneously. In this investigation, we address this contradictory issue of LiMn(2)O(4) by developing a truncated octahedral structure in which most surfaces are aligned to the crystalline orientations with minimal Mn dissolution, while a small portion of the structure is truncated along the orientations to support Li diffusion and thus facilitate high discharge rate capabilities. When compared to control structures with much smaller dimensions, the truncated octahedral structure as large as 500 nm exhibits better performance in both discharge rate performance and cycle life, thus resolving the previously conflicting aspects of LiMn(2)O(4).

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 ...