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In this work, highly soluble LiNO 3 was adopted as the neutrally aqueous electrolyte for active carbon (AC)-based electrochemical double-layer capacitors (EDLCs), of which the electrochemical performances were evaluated. Simultaneously, the physicochemical properties such as the ionic conductivity and viscosity of the LiNO 3 aqueous solution were investigated. As compared with the most studied Li 2 SO 4 aqueous solution, the LiNO 3 aqueous solution displays more favorable physicochemical properties and electrochemical performances as the neutral electrolytes for EDLCs. To be specific, the conductivity of the 5.0 M LiNO 3 aqueous solution can reach up to 154.8 mS cm −1  at 25 °C, which is nearly two times of the maximum conductivity of 77.6 mS cm −1 for the 2.0 M Li 2 SO 4 aqueous solution under the identical testing conditions. Even at a concentration as high as 9.0 M, the absolute viscosity of the LiNO 3 aqueous solution is only 2.4, while that of the Li 2 SO 4 aqueous solution achieves 3.0 at the maximum concentration of 2.5 M. Additionally, 5.0 M LiNO 3 aqueous solution exhibits a wide electrochemical potential stability window from −0.9 to 0.9 V (vs. SCE) at the AC electrode, giving rise to an operating cell voltage of 1.8 V, which is comparable to that of 2.0 M Li 2 SO 4 aqueous solution. Further, with the 5.0 M LiNO 3 aqueous solution as the electrolyte, the as-fabricated EDLC delivers an energy density up to 21.16 Wh Kg −1  at a power density of 100.09 W kg −1 , which is higher than 18.43 Wh Kg −1 for the EDLC with the 2.0 M Li 2 SO 4 aqueous electrolyte at the identical power density. Even though the power density reaches as high as 5970 W kg −1 , the energy density of the EDLC with the 5.0 M LiNO 3 aqueous electrolyte can still remain at 13.1 Wh Kg −1 , substantially higher than 8.71 Wh Kg −1 of the EDLC with the 2.0 M Li 2 SO 4 aqueous electrolyte at the same power density. Moreover, the EDLC with the 5.0 M LiNO 3 aqueous electrolyte also holds good cyclic stability. After 10000 charge–discharge cycles at a current density of 1 A g −1 and a cut-off voltage of 1.8 V, the capacity retention of this EDLC retains more than 90%. These results can render an insight to explore safe, eco-friendly, inexpensive and neutrally aqueous electrolytes for supercapacitors. [ABSTRACT FROM AUTHOR]

Although hard carbon (HC) demonstrates superior initial Coulombic efficiency, cycling durability, and rate capability in ether-based electrolytes compared to ester-based electrolytes for sodium-ion batteries (SIBs), the underlying mechanisms responsible for these disparities remain largely unexplored. Herein, ex situ electron paramagnetic resonance (EPR) spectra and in situ Raman spectroscopy are combined to investigate the Na storage mechanism of HC under different electrolytes. Through deconvolving the EPR signals of Na in HC, quasi-metallic-Na is successfully differentiated from adsorbed-Na. By monitoring the evolution of different Na species during the charging/discharging process, it is found that the initial adsorbed-Na in HC with ether-based electrolytes can be effectively transformed into intercalated-Na in the plateau region. However, this transformation is obstructed in ester-based electrolytes, leading to the predominant storage of Na in HC as adsorbed-Na and pore-filled-Na. Furthermore, the intercalated-Na in HC within the ether-based electrolytes contributes to the formation of a uniform, dense, and stable solid-electrolyte interphase (SEI) film and eventually enhances the electrochemical performance of HC. This work successfully deciphers the electrolyte-dominated Na + storage mechanisms in HC and provides fundamental insights into the industrialization of HC in SIBs., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

N-doped carbon coated TiO 2 nanoparticles (TiO 2 @NC) were synthesized through a simple two-step route, in which dopamine was simultaneously utilized as both nitrogen and carbon sources. With TiO 2 @NC applied in the Na-ion battery (SIB) anodes, the continuous and uniform N-doped carbon layer can not only enhance the electrical conductivity of TiO 2 and facilitate the surface pseudocapacitive process, but also serve as a buffer layer to accommodate the volume expansion during the sodiation-desodiation processes. The as-prepared TiO 2 @NC exhibits excellent electrochemical performance when utilized as the SIB anodes, which delivers a remarkably high reversible capacity of 250.2 mAh g -1 at a rate of 0.25C (84 mA g -1 ) after 200 cycles and still retains 122.1 mAh g -1 at 10C (3.35 A g -1 ) even after 3000 cycles accompanied with a 95.3% retention of the maximum capacity, outperforming most of the reported TiO 2 /C-based composites as SIB anodes. To our best knowledge, the preparation of TiO 2 @NC with dopamine as both nitrogen and carbon sources and its application in the SIB anodes are reported for the first time., (Copyright © 2018 Elsevier Inc. All rights reserved.)