Studies on MgNi-Based Metal Hydride Electrode with Aqueous Electrolytes Composed of Various Hydroxides

Abstract

Abstract:Compositions of MgNi-based amorphous-monocrystalline thin films produced by radio frequency (RF) sputtering with a varying composition target have been optimized. The composition Mg 52 Ni 39 Co 3 Mn 6 is identified to possess the highest initial discharge capacity of 640 mAh·g −1 with a 50 mA·g −1 discharge current density. Reproduction in bulk form of Mg 52 Ni 39 Co 3 Mn 6 alloy composition was prepared through a combination of melt spinning (MS) and mechanical alloying (MA), shows a sponge-like microstructure with >95% amorphous content, and is chosen as the metal hydride (MH) alloy for a sequence of electrolyte experiments with various hydroxides including LiOH, NaOH, KOH, RbOH, CsOH, and (C 2 H 5 ) 4 N(OH). The electrolyte conductivity is found to be closely related to cation size in the hydroxide compound used as 1 M additive to the 4 M KOH aqueous solution. The degradation performance of Mg 52 Ni 39 Co 3 Mn 6 alloy through cycling demonstrates a strong correlation with the redox potential of the cation in the alkali hydroxide compound used as 1 M additive to the 5 M KOH aqueous solution. NaOH, CsOH, and (C 2 H 5 ) 4 N(OH) additions are found to achieve a good balance between corrosion and conductivity performances.

Effects of Cs2CO3 Additive in KOH Electrolyte Used in Ni/MH Batteries

“…The AR3 MH alloy is very reactive to the KOH electrolyte due to the alloy's high content of Mg and the high porosity caused by the mechanical alloying preparation [12]. A rapid decay in the KOH electrolyte was previously reported [5,6,12]. Figure 2 shows an increase in initial discharge capacity and a decrease in capacity decay with the addition of Cs 2 CO 3 .…”

“…The effects of Cs 2 CO 3 on the AR3 alloy electrode performances are shown in Figure 2. The AR3 MH alloy is very reactive to the KOH electrolyte due to the alloy's high content of Mg and the high porosity caused by the mechanical alloying preparation [12]. A rapid decay in the KOH electrolyte was previously reported [5,6,12].…”

“…Therefore, the 6.44 M KOH + 0.33 M Cs2CO3 electrolyte has a decreased resistance and increased conductivity. While a low Cs2CO3 concentration promotes proton transfer in the system and improves both the discharge capacity and cycling performance, a higher Cs2CO3 concentration increases the solution resistivity due to the increased concentrations of larger cations (Cs + ) and anions (CO3 2− ) in the electrolyte, according to Stokes' Law [12].…”

Research in Nickel/Metal Hydride Batteries 2017

“…In 2016, we reported that the reduction of the corrosion nature of the alkaline KOH electrolyte can be accomplished by selection of both adequate combination of alkaline species [22] and salt additives [23]. In this Special Issue, the effects of adding Cs 2 CO 3 salt in the electrolyte was further investigated, and a newly formed surface amorphous oxide was credited for the reduction of surface oxidation of the MgNi-based MH alloy [24].…”

New Type of Alkaline Rechargeable Battery—Ni-Ni Battery

“…The Ni segregation is more severe during slower rate discharges and needs to be controlled to sustain the initial capacity. Approaches for such segregation-prevention may include implantation of grain growth inhibitor [40], control of oxygen impurities [41], addition of elements with different solubilities among phases [42], addition of rare earth elements [43], addition of other transition metals with larger ionic radii, introduction of a pulse charge/discharge method to interrupt the formation of Ni(OH) 2 isolated grain, surface modification with surfactant to make it more difficult to precipitate into larger Ni(OH) 2 grains, a new combination of alkali [44] and salt [45] used in the electrolyte, and improvements in the co-precipitation process to evenly distribute the cation in the hydroxide. discussed in Section 3.1.…”