Recently, LiNO3-based electrolytes using tetraglyme (G4) solvent (LiNO3/G4) have attracted increasing attention for non-aqueous rechargeable Li-air (O2) batteries (LAB) because of the bifunctional effect of NO3 − anion as both redox mediator (RM) at air electrode and additive to form Li2O layer on the surface of Li metal negative electrode (NE), which suppresses Li dendrite growth and electrolyte decomposition. However, the dissociation degree of LiNO3 salt was quite low, which causes to low ionic conductivity and the above effects of NO3 − would not work effectively in the electrolyte. In this study, we tried to apply dual solvent system to the LiNO3/G4 electrolyte. Namely, acetonitrile and dimethyl sulfoxide (DMSO) with relatively high dielectric constant and low viscosity were mixed with G4 solvent to increase the number per volume and mobility of Li+ and NO3 − as carrier ions for reduction of the large overpotential during charge process and enhancement of the power density. The DMSO mixed electrolyte greatly reduced the large charge overpotential and relative stable operation for the LAB (Li ∣ O2) cells. Furthermore, the Li2O passivation layer formed by NO3 − anion effectively suppressed the electrolyte decomposition at Li metal NE. These effects were enhanced especially at higher rate of discharge/charge operation.
Acid-treated Ketjen Black (a-KB) carbon supports were prepared to investigate how oxidation of the carbon surface influences La 0.6 Sr 0.4 MnO 3 (LSM) nanoparticle distribution, and conjugation to the carbon support. 30 wt.% LSMloaded a-KB (LSM/a-KB) materials were prepared as air-electrode catalysts for rechargeable lithium-air batteries (LABs). a-KB exhibited a significant degree of O-containing (C-O, COO) surface functional groups, which resulted in the formation of smaller LSM nanoparticles and enhanced homogeneity over the carbon support when compared with the pristine KB support. Consequently, C-O-Mn bonds were formed, which increased the Mn oxidation state, and concomitantly enhanced conjugation resulting in improved catalytic activity. Additionally, the overpotential was reduced during charging (Li 2 O 2 decomposition). Furthermore, LSM/a-KB enhanced the cyclability of the LAB test cell. Scanning electron microscopy observations revealed that LSM/a-KB efficiently decomposed the Li 2 O 2 deposition layer, even after the 15th charge cycle when compared with LSM/KB. The LSM/a-KB air-electrode exhibited a more homogeneous and smaller-sized (and/or amorphous) Li 2 O 2 deposition after discharging. Therefore, the oxidation of the carbon surface, resulting in enhanced LSM nanoparticle distribution on, and conjugation to, the a-KB surface, influences the homogeneity of the Li 2 O 2 deposition onto the support during the discharge process leading to its facile decomposition during the following charge process.
Li−air batteries (LAB) have a theoretical energy density as high as 3500 Wh kg ̶ 1 ; however, many problems remain to be addressed before their practical application.Introduction of a redox mediator (RM) is commonly applied to reduce the high overpotential of the air electrode (AE) during the charge process. We try to fix an RM on the AE by coating it with a slurry of carbon black and binder on a carbon paper substrate to enable us not only to suppress the shuttle effect but also to concentrate the RM on the surface of the AE where it works. We use LiBr as the RM in this study and compare two types of LAB cells: one with a LiBr-coated AE and the other with LiBr dissolved in the electrolyte solution. The cell with the LiBr-coated AE exhibits a better cell performance than that with the dissolved LiBr.
LiNO3 has been widely studied as a redox mediator to reduce positive electrode overvoltage during charging of lithium/air (O2) batteries. LiNO3 has a bifunctional effect as a redox mediator for the positive electrode and as a surface modifier for the lithium negative electrode. The dissociation of LiNO3 electrolyte salt was enhanced by using a mixed solvent of tetraglyme and a sulfone with a high dielectric constant. This extended the charging voltage plateau because the mixed solvent enhanced the oxidation of NO 2 − into NO2 in the 1.0 M LiNO3 electrolyte solution. The viscosities of the sulfone-containing electrolyte solutions decreased and their ionic conductivities increased as the temperature increased. Therefore, Walden plots for the electrolyte solutions containing sulfones were parallel to the ideal line, meaning that the dissociation of LiNO3 was unaffected by temperature due to the strong solvation of ethyl methyl sulfone and tetramethylene sulfone to Li+ ions. Consequently, the sulfone-containing electrolyte solutions delivered better charging performance than an electrolyte solution of simple tetraglyme at 50 °C.
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