Antonio B. Fuertes

Carbon-encapsulated γ-Fe ₂ O ₃ nanoparticles (NPs) exhibit emerging magnetic proximity effects together with a robust exchange-bias.

Invited for this month's cover picture is the group of Dr. Noel Díez. The Front Cover illustrates the use of monodisperse, highly porous carbon nanoparticles derived from polypyrrole as the electrode material in high power supercapacitors. The highly porous nanoparticles were employed to construct supercapacitors with practical mass loadings that showed a fast response in different types of electrolyte systems. Read the full text of the Article at 10.1002/batt.202100169.

The entangled core/shell magnetic structure of Cr ₂ O ₃ nanoparticles, where pinned uncompensated spins at the shell are randomly distributed in a low-temperature spin-glass ordering, gives rise to a Double Exchange-bias mechanism.

Highly porous carbon nanoparticles are very suitable materials for supercapacitor electrodes due to their combination of large surface area for ion adsorption and short pathways for fast ion diffusion. Herein we describe the synthesis of highly porous carbon nanospheres (d=90 nm) by a simple strategy that involves the preparation of monodisperse nanoparticles by the oxidative polymerization of pyrrole, followed by their direct chemical activation with KHCO_3. The morphology of the nanospheres is well retained after activation, and the inorganic impurities are removed by a simple washing step with water. The porous nanospheres possess a high electrical conductivity and specific surface areas exceeding 3000 m² g⁻¹ due to their high content of micropores and small mesopores (2SO₄ electrolyte, the porous nanospheres reach a capacitance of 262 F g⁻¹ and withstand an ultrahigh current density of 80 A g⁻¹ maintaining a capacitance above 100 F g⁻¹. In the organic 1 M TEABF₄/AN and EMImTFSI/AN electrolytes, the nanoparticles reach 175 and 155 F g⁻¹, and the supercapacitors could be cycled up to 50 A g⁻¹ delivering 30 Wh kg⁻¹ at a power density of 20 kW kg⁻¹ and 31 Wh kg⁻¹ at a power density of 31 kW kg⁻¹, respectively. These results demonstrate the potential of these nanoparticles for energy storage applications.

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less‐corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self‐activation methodologies applied to organic salts and biomass products is also discussed.

Polysulfide shuttle effects, active material losses, formation of resistive surface layers and continuous electrolyte consumption create a major barrier for the lightweight and low-cost lithium-sulfur (Li-S) battery adoption. Tuning electrolyte composition by using additives and most importantly by substantially increasing electrolyte molarity was previously shown to be one of the most effective strategies. Contrarily, little attention has been paid to dilute and super-diluted LiTFSI/DME/DOL/LiNO3 based-electrolytes, which have been thought to aggravate the polysulfide dissolution and shuttle effects. Here we challenge this conventional wisdom and demonstrate outstanding capabilities of a dilute (0.1 mol L-1 of LiTFSI in DME/DOL with 1 wt.% LiNO3) electrolyte to enable better electrode wetting, greatly improved high-rate capability and stable cycle performance for high sulfur loading cathodes and low electrolyte/sulfur ratio in Li-S cells. Overall, the presented study shines light on the extraordinary ability of such electrolyte systems to suppress short-chain polysulfide dissolution and polysulfide shuttle effects.

An upgrade of the scalable fabrication of high-performance sulfur-carbon cathodes is essential for the widespread commercialization of this technology. Herein we present a simple, cost-effective and scalable approach for the fabrication of cathodes comprising sulfur and high-surface area, N,S-codoped carbons. The method involves the use of a sulfur salt, i.e. sodium thiosulfate, as activating agent, sulfur precursor and S-dopant, and polypyrrole as carbon precursor and N-dopant. In this way, the production of the porous host and the incorporation of sulfur are combined in the same procedure. The porous hosts thus produced have BET surface areas in excess of 2000 m² g⁻¹, a micro-mesoporous structure, as well as sulfur and nitrogen contents of 5–6 wt% and ~2 wt%, respectively. The elemental sulfur content in the composites can be precisely modulated in the range of 24 to ca. 90 wt% by controlling the amount of sodium thiosulfate used. Remarkably, these porous carbons are able to accommodate up to 80 wt% sulfur exclusively within their porosity. When analyzed in lithium-sulfur batteries, these sulfur-carbon composites show high specific capacities of 1100 mAh g⁻¹ at a low C-rate of 0.1 C and above 500 mAh g⁻¹ at a high rate of 2 C for sulfur contents in the range of 50–80 wt%. Remarkably, the composites with 51–65 wt% S can still provide above 400 mAh g⁻¹ at an ultra-fast rate of 4 C (where a charge and discharge cycle takes only ten minutes). The good rate capability and sulfur utilization was additionally assessed for cathodes with a high sulfur content (65–74%) and a high sulfur loading (>5 mg cm⁻²). In addition, cathodes of 4 mg cm⁻² successfully cycled for 260 cycles at 0.2 C showed only a low loss of 0.12%/cycle.