Ammonium Ionic Liquid-Functionalized Phenothiazine as a New Redox Mediator for High Chemical Stability on the Anode Surface in Lithium–Air Batteries

Abstract

The application of redox mediators (RMs) as soluble catalysts can address the problem of insufficient contact between conventional solid catalysts for lithium–air batteries (LABs). However, oxidized RM molecules migrate to the lithium anode and react with lithium, which results in the accumulation of surface corrosion products that weaken the redox activity of the RM. This paper presents a new combination of phenothiazine (PTZ) as an RM and an ammonium–based ionic liquid (IL) source as a protective agent to prevent the side reactions with lithium and to enhance the electrochemical performance of LABs. IL-functionalized PTZ (IL-PTZ) was successfully synthesized through N-alkylation, quaternization, and anion–exchange reactions. IL-PTZ improved the chemical stability of the RM molecules on the lithium surface as well as the electrochemical performance. A microstructural analysis revealed that the IL group in the IL-PTZ molecules facilitated smooth lithium stripping/plating by blocking the side reactions between the RM and lithium. Compared with the LAB with the PTZ electrolyte, that with the IL-PTZ electrolyte exhibited a significantly higher discharge capacity (2500 mA h/g vs 1500 mA h/g) and a cycle life that was 2 times longer. The IL-PTZ molecule was demonstrated to exhibit great potential as a novel soluble catalyst for application in high-performance LABs.

Activity of N–H in phenothiazine derivatives: synthesis and applications in fluoride ions sensing and electrochromism

“…Therefore, substitution with moieties with different electron-donating abilities has very little effect on the reduction potential of the phenothiazine derivatives and the relatively low LUMO (lowest unoccupied molecular orbital) energy levels. 28,49 However, mutual orthogonalization of the substituent groups indicates that the electrophilic -CN group is effective and even causes a shift of the anodic reduction potential of 3c. The highest occupied molecular orbital (HOMO) levels, as calculated from the LUMO levels and the optical band gaps (3a, 2.86 eV; 3b, 2.98 eV; 3c, 2.81 eV; 3d, 2.99 eV), were À6.51, À6.70, À6.45 and À6.59 eV, respectively, mimic the trend shown by the calculated values.…”

“…23–27 However, most these photoactive materials use the protected PTZ structure (N-substituted phenothiazine derivatives), in which the nitrogen atom at the 10-position (10 N–H) is replaced by a covalent group. 28–30…”

“…[23][24][25][26][27] However, most these photoactive materials use the protected PTZ structure (N-substituted phenothiazine derivatives), in which the nitrogen atom at the 10-position (10 N-H) is replaced by a covalent group. [28][29][30] Because of its highest charge density and Lewis basic nature, fluoride has received well-deserved attention from the scientific community owing to its association with a diverse array of biological, medical, and technological processes. [31][32][33] Since the fluoride ion is a strong hydrogen bond acceptor, a large number of optical sensors have been developed based on fluoride induced deprotonation through H-bonding for detecting fluoride ions.…”

Li–O2/Air Batteries Using Ionic Liquids – A Comprehensive Review

“…This was attributed to the inhibition of side reactions by IL between RM and Li metal. [ 114 ] Tkacheva et al also incorporated 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)IL electrolyte in LOB and achieved low charge overpotential (0.6 V) and 50 stable cycles. The enhanced performance of RM functionalized IL is attributed to their synergistic effect in stabilizing the superoxide radical and suppressing parasitic side reactions.…”

Thin, Flexible, and High-Performance Solid-State Polymer Electrolyte Membranes for Li–O2 Batteries

“…Many researchers have tried to surmount the shortcomings of SSEs such as poor electrolyte–electrode interfacial contact, poor flexibility, low conductivity, and poor electrochemical stability. , Although these breakthroughs provide clues for SSLOBs, there are still unsolved bottlenecks. First, the large voltage gap between charge and discharge gives rise to severely low energy efficiencies. − It is thus necessary to avoid a high charging voltage of over 4.0 V and side reactions during charging. , Second, in SSLOBs, high mechanical strength is needed to suppress the dendritic growth of lithium and reduce the electrolyte membrane thickness for high gravimetric/volumetric energy density.…”