We investigated herein the morphological, structural, and electrochemical features of electrodes using a sulfur (S)-super P carbon (SPC) composite (i.e., S@SPC-73), and including few-layer graphene (FLG), multiwalled carbon nanotubes (MWCNTs), or a mixture of them within the current collector design. Furthermore, we studied the effect of two different electron-conducting agents, that is, SPC and FLG, used in the slurry for the electrode preparation. The supports have high structural crystallinity, while their morphologies are dependent on the type of material used. Cyclic voltammetry (CV) shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization. This activation process is verified by electrochemical impedance spectroscopy (EIS) with a decrease of the resistance after the first CV scan. Furthermore, CV at increasing scan rates indicates a Li+ diffusion coefficient (D) ranging between 10−9 and 10−7 cm2·s−1 in the various states of charge of the cell, and the highest D value for the electrodes using FLG as electron-conducting agent. Galvanostatic tests performed at constant current of C/5 (1 C = 1675 mA·gS−1) show high initial specific capacity values, which decrease during the initial cycles due to a partial loss of the active material, and subsequently increase due to the activation process. All the electrodes show a Coulombic efficiency higher than 97% upon the initial cycles, and a retention strongly dependent on the electrode formulation. Therefore, this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology, mechanical stability, and promising electrochemical performance in practical Li-S cells.

A safe lithium-sulfur (LiÀ S) battery employs a composite polymer electrolyte based on a poly(ethylene glycol) dimethyl ether (PEGDME) solid at room temperature. The electrolyte membrane enables a stable and reversible LiÀ S electrochemical process already at 50 °C, with low resistance at the electrode/ electrolyte interphase and fast Li + transport. The relatively low molecular weight of the PEGDME and the optimal membrane composition in terms of salts and ceramic allow a liquid-like LiÀ S conversion reaction by heating at moderately high temperature, still holding the solid-like polymer state of the cell. Therefore, the electrochemical reaction of the polymer LiÀ S cell is characterized by the typical dissolution of lithium polysulfides into the electrolyte medium during discharge and the subsequent deposition of sulfur at the electrode/electrolyte interphase during charge. On the other hand, the remarkable thermal stability of the composite polymer electrolyte (up to 300 °C) suggests a lithium-metal battery with safety content significantly higher than that using the common, flammable liquid solutions. Hence, the LiÀ S polymer battery delivers at 50 °C and 2 V a stable capacity approaching 700 mAh g S À 1 , with a steady-state coulombic efficiency of 98 %. These results suggest a novel, alternative approach to achieve safe, highenergy batteries with solid polymer configuration.

Herein we investigate a lowly flammable electrolyte formed by dissolving sodium trifuoromethansulfonate (NaCF3SO3) salt in triethylene glycol dimethyl ether (TREGDME) solvent as suitable medium for application in Na-ion and Na-S cells. The study, performed by using various electrochemical techniques, including impedance spectroscopy, voltammetry, and galvanostatic cycling, indicates for the solution high ionic conductivity and sodium transference number (t +), suitable stability window, very low electrode/electrolyte interphase resistance and sodium stripping/deposition overvoltage. Direct exposition to flame reveals the remarkable safety of the solution due to missing fire evolution under the adopted experimental setup. The solution is further investigated in sodium cells using various electrodes, i.e., mesocarbon microbeads (MCMB), tin-carbon (Sn-C), and sulfur-multiwalled carbon nanotubes (S-MWCNTs). The results show suitable cycling performances, with stable capacity ranging from 90 mAh g −1 for MCMB to 140 mAh g −1 for Sn-C, and to 250 mAh g −1 for S-MWCNTs, as an important additional bonus for enhancing the battery safety level [29-31]. A room-temperature rechargeable sodium-ion battery was formed by coupling the layered P2-Na0.7CoO2 cathode with the graphite anode in an electrolyte formed by NaClO4 salt in tetraethylene glycol dimethyl (TEGDME) [32]. This rocking chair cell, operating though sodium intercalation/de-intercalation processes within the cathode and anode layers, has shown suitable electrode/electrolyte interphase, and excellent performance in terms of cycle life, efficiency, and power capability [32]. A rechargeable sodium-oxygen cell has been reported to efficiently operate at room temperature employing a cathode formed by multiwalled carbon nanotubes (MWCNTs) cast on a gas diffusion layer in a TEGDME-NaCF3SO3 electrolyte solution [33]. The above Na/O2 cell has shown charge-discharge polarization as low as 400 mV, a capacity of 500 mAh g −1 and an energy efficiency of 83% for several cycles [33]. Diethylene glycol dimethyl ether (DEGDME) dissolving NaCF3SO3 has been used as the electrolyte in a room temperature sodium-sulfur cell using a S-MWCNTs composite, revealing average working voltage of about 1.8 V and a specific capacity of the order of 500 mAh g −1 [17], while a sodium-ion cell combining nanostructured Sn-C anode and hollow carbon spheres-sulfur (HCS-S) cathode in a TEGDME-NaCF3SO3 electrolyte revealed remarkable capacity of 550 mAh g −1 and theoretical energy density of 550 Wh kg −1 [34]. These encouraging results have suggested the use of glyme-based electrolytes as the preferred electrolyte media for a series of very attracting energy storage systems based on sodium, including Na-ion, Na/S and Na/O2 batteries. Therefore, in this work we investigate a solution formed by dissolving NaCF3SO3 in triethylene glycol dimethyl ether (TREGDME) as suitable electrolyte for sodium battery. The solution is studied by various electrochemical techniques in order to determine its ionic conductivi...

The effects of a biomass-derived hard carbon matrix and a sustainable cross-linked binder are investigated as electrode components for a silicon-based anode in lithium-ion half-cells, in order to reduce the capacity fade due to volume expansion and shrinkage upon cycling. Ex situ Raman spectroscopy and impedance spectroscopy are used to deeply investigate the structural and interfacial properties of the material within a single cycle and upon cycling. An effective buffering of the volume changes of the composite electrode is evidenced, even at a high Si content up to 30% in the formulation, resulting in the retention of structural and interfacial integrity. As a result, a high capacity performance and a very good rate capability are displayed even at high current densities, with a stable cycling behavior and low polarization effects.

A solid polymer electrolyte has been developed and employed in lithium‐metal batteries of relevant interest. The material includes crystalline poly(ethylene glycol)dimethyl ether (PEGDME), LiTFSI and LiNO3 salts, and a SiO2 ceramic filler. The electrolyte shows ionic conductivity more than 10−4 S cm−1 at room temperature and approaching 10−3 S cm−1 at 60 °C, a Li+‐transference number exceeding 0.3, electrochemical stability from 0 to 4.4 V vs. Li+/Li, lithium stripping/deposition overvoltage below 0.08 V, and electrode/electrolyte interphase resistance of 400 Ω. Thermogravimetry indicates that the electrolyte stands up to 200 °C without significant weight loss, while FTIR spectroscopy suggests that the LiTFSI conducting salt dissolves in the polymer. The electrolyte is used in solid‐state cells with various cathodes, including LiFePO4 olivine exploiting the Li‐insertion, sulfur–carbon composite operating through Li conversion, and an oxygen electrode in which reduction and evolution reactions (i. e., ORR/OER) evolve on a carbon‐coated gas diffusion layer (GDL). The cells operate reversibly at room temperature with a capacity of 140 mA h g−1 at 3.4 V for LiFePO4, 400 mA h g−1 at 2 V for sulfur electrode, and 500 mA h g−1 at 2.5 V for oxygen. The results suggest that the electrolyte could be applied in room‐temperature solid polymer cells.