The Double-Edged Effect of Water on Li-O₂ Aprotic Batteries

Abstract

Storing larger amounts of energy is becoming critical as more renewable and intermittent energy sources emerge in our society. Li-O2 batteries have the highest theoretical energy density, but there are still barriers to overcome. The presence of water in atmospheric air makes studying its effects on battery performance necessary if ambient oxygen is to be used in such devices. This paper investigates the effect of different water concentrations in the electrolyte of Li-O2 aprotic batteries, on deep discharge capacity and cyclability. Batteries were prepared with a metallic lithium anode, glass microfiber membrane, 0.1 M LiClO4/DMSO electrolyte with various water concentrations (15-144,000 ppm), and carbon paper cathode. An increase in discharge capacity of >300% was achieved with 550 ppm of water; however, a gradual reduction in cyclability was observed increasing water concentration. We show that this occurs due to changes in the reaction mechanism, composition and morphology of the discharge products, incomplete decomposition, and formation of a passivating film on the metallic lithium anode. In addition, we elucidate the causes underlying the involved mechanism and highlights the double-edged effect of water on the electrochemical performance of Li-O2 batteries, causing improvements in deep discharge capacity at the cost of reduced cyclability.

Mixture of an ionic liquid and organic solvent at graphene: interface structure and ORR mechanism

“…At the same time, when the reaction proceeds according to the solution-mediated pathway, large toroidal particles of Li 2 O 2 are formed, increasing the discharge capacity. However, in this case, worse battery cycling and rapid degradation of electrodes and electrolytes are reported, [12][13][14] which is associated in recent works with an increased overpotential of the battery recharge, accelerating parasitic reactions, as well as the formation of extremely reactive singlet oxygen during the disproportionation of LiO 2 . 8,[15][16][17] However, the precise mechanism of singlet oxygen formation remains still unclear.…”