Abstract
KOH-based electrolytes with different salt additives were investigated to reduce their corrosive nature toward Mg/Ni metal hydride alloys used as negative electrodes in nickel metal hydride (Ni/MH) batteries. Alkaline metal halide salts and oxyacid salts were studied as additives to the traditional KOH electrolyte with concentrations varying from 0.005 M to 1.77 M. Effects of the cations and anions of the additives on charge/discharge performance are discussed. The reduction potential of alkaline cations and radii of halogen anions were correlated with initial capacity and degradation of the metal hydride alloy. A synergistic effect between KOH and some oxyacid salt additives was observed and greatly influenced by the nature of the salt additives. It was suggested that both the formation of a solid film over the metal hydride surface and the promotion of proton transfer in the additives containing electrolytes led to a decreased degradation of the electrodes and an increased discharge capacity. 12 salt additives, NaC2H3O2, KC2H3O2, K2CO3, Rb2CO3, Cs2CO3, K3PO4, Na2WO4, Rb2SO4, Cs2SO4, NaF, KF, and KBr, were found to increase the corrosion resistance of the MgNi-based metal hydride alloy.
Highlights
Nickel metal hydride (Ni/MH) batteries are currently one of the most widely used energy storage devices with many applications including hybrid electric vehicles, vacuum cleaners, electric toys, power tools, cordless phones, etc. [1,2]
The cycle stability and capacity/degradation as functions of KOH concentration of negative electrode composed of Mg52Ni39Co3Mn6 MH alloy in a traditional 30% KOH electrolyte are shown in Figures 1 and 2, respectively
Discharge capacity is closely related to the amount of MgNi metal hydride in negative electrodes. This solid film over the MgNi metal hydride particles could physically protect the electrode from electrolyte corrosion; (2) H-transfer is promoted in aqueous electrolyte
Summary
Nickel metal hydride (Ni/MH) batteries are currently one of the most widely used energy storage devices with many applications including hybrid electric vehicles, vacuum cleaners, electric toys, power tools, cordless phones, etc. [1,2]. Nickel metal hydride (Ni/MH) batteries are currently one of the most widely used energy storage devices with many applications including hybrid electric vehicles, vacuum cleaners, electric toys, power tools, cordless phones, etc. [1,2] They have many advantages such as having a high specific power, excellent tolerance to abuse, long cycle life, wide temperature operation range, and low self-discharge. A basic Ni/MH battery consists of an assembly of a highly conductive electrolyte, a metal hydride (MH) negative electrode, and a nickel hydroxide positive electrode. The cell reactions on the electrodes are shown in following equations: Negative electrode: M + H2O + e− ⇌ OH− + MH (1)
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