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Trapping lithium polysulfides formed in the sulfur positive electrode of lithium-sulfur batteries is one of the promising approaches to overcome the issues related to polysulfide dissolution. In this work, we demonstrate that intrinsically hydrophilic magnesium oxide (MgO) nanoparticles having surface hydroxyl groups can be used as effective additives to trap lithium polysulfides in the positive electrode. MgO nanoparticles were uniformly distributed on the surface of the active sulfur, and the addition of MgO into the sulfur electrode resulted in an increase in capacity retention of the lithium-sulfur cell compared to a cell with pristine sulfur electrode. The improvement in cycling stability was attributed to the strong chemical interactions between MgO and lithium polysulfide species, which suppressed the shuttling effect of lithium polysulfides and enhanced the utilization of the sulfur active material. To the best of our knowledge, this report is the first demonstration of MgO as an effective functional additive to trap lithium polysulfides in lithium-sulfur cells.

The critical issues that hinder the practical applications of lithium-sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium-sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g (corresponding to an areal capacity of 3.2 mAh cm) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate.

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Over the past decades, there has been tremendous progress to overcome the intrinsic issues of lithium metal batteries (LMBs). In particular, studies have shown that utilizing lithiophilic materials for LMBs...

Electrochemical ultracapacitors exhibiting high energy output and an ultra-long cycle life, utilizing green and sustainable materials, are of paramount importance for next-generation applications.

raises questions on their future use in large-scale energy storage devices. [2,4] Sodium-ion capacitors (NICs) are promising alternative devices owing to the wide availability of sodium resources and their competence for demonstrating higher performance than LICs. [5,6] NICs are fabricated by coupling a battery-type faradic electrode that stores sodium ions along with an electrical double-layer capacitor (EDLC)-type porous carbon electrode that stores anions simultaneously via quick surface adsorption. [7,8] NICs that exhibit enhanced energy retention at high power along with low energy loss per cycle is extensively under research.To date, several NICs have been studied and demonstrated a remarkable gravimetric energy-power performance usually at low mass loading conditions. For practical applications, a high volumetric performance with high mass loading is crucial. But it faces several major challenges: (i) high active mass loading leads to poor electrolyte penetration deeper into thicker electrodes and thereby making causing severe ionic diffusion and electron transport losses, (ii) achieving a high stability and high rate performance at high mass loading conditions is difficult as a small morphology change could simulate electrode cracking or peeling from current collectors, (iii) very high amount of conductive carbon in battery-type electrode and carbon itself as battery-type electrode greatly decreases the volumetric performance. [9][10][11][12][13] Furthermore, safety issues related to liquid electrolyte inflammability, and leakage must be seriously addressed with an alternative. [14][15][16][17][18][19] Battery electrodes in NICs primarily use intercalationtype compounds such as hard carbon, NaTi 2 (PO 4 ) 3 , NiCo 2 O 4 , Na 2 Fe 2 (SO 4 ) 3 , and Na 3 Ti 2 O 7 . [20][21][22][23] The sluggish diffusioncontrolled sodium-ion storage in these compounds enables insertion of a limited number of sodium ions into the battery electrode at higher power and, lowers the energy output. [24][25][26] However, utilizing the strategy of sodium-ion storage on the surface of the battery electrode by quick surface pseudocapacitance is advantageous over diffusion-controlled bulk storage. [27][28][29] NICs driven by cationic surface pseudocapacitive intercalation could deliver superior energy, especially at high power, along with longer cycle life even under high mass loading conditions. The new approach could boost both the gravimetric and The sodium-ion capacitor (NIC) represents an important research approach to bridge the gap between batteries and capacitors, but is still limited by inferior energy behavior at high power, low volumetric performance, low electrode mass loading, and safety issues with conventional liquid electrolyte. Herein, a high-performing, kinetically superior, and safer quasi-solid-state NIC utilizing the fast sodium storage in TiO 2 and rapid ion adsorption on a biomassderived porous carbon with a sodium-ion conducting P(VDF-HFP) gel polymer electrolyte is presented. Owing to high mass loading, low gr...