The Influence Of Coating And Evolution Of Nd-Mg-Ni Alloy On Electrochemical Properties

Nd–Mg–Ni-based hydrogen storage alloys are supposed to be used as high capacity negative material of Ni/MH battery because of their higher capacity and lower cost.In t he charge-discharge process of the Ni/MH battery,alkali is necessary as electrolyte.However,the Nd-Mg-Ni alloys are easily corroded by the electrolyte,and they are oxidized and pulverized,resulting in decline of the battery performance and the failure to use the battery for a long time.In order to improve this phenomenon,the surface treatment technology is used to coat polyaniline layer,reduced graphene oxide layer and rGO/Cu composite layer on the surface of Nd-Mg-Ni alloys to improve the surface state of hydrogen storage alloy,so as to improve the electrochemical performance of the alloy.The surface of alloy was coated with a layer of PANI film via an evaporationpolymerization treatment.As the coating time increases,the coating PANI layers become thicker.As PANI coating was performed for 10 min,the discharge capacity and the discharge platform voltage are both higher than the other alloy electrodes.As PANI coating was performed for 45 min,the high rate discharge performance is the best,and it reaches 79.4% at a discharge current density of 1500 mA/g.The alloy electrode treated for 30 min shows a better cycling stability,and the discharge capacity retention is as high as 95.2%.The surface of alloy was coated with a layer of rGO after graphene oxide treatment.With the increase of the concentration of graphene oxide solution,the coating became thicker.As the concentration is 0.1g/L,the overall electrochemical properties are much better.The high rate discharge performance increases from 53.2% to 83.9% at discharge current density of 1500 mA/g,30.7% higher.The median discharge voltage increases from 1.210 V to 1.249 V,increased by 0.039 V.After 100 cycles the discharge capacity loss is reduced from 37.5 mAh/g to 28.8 mAh/g.The SEM results of rGO/Cu coated alloy show that a uniform coating of reduced graphene oxide and copper is formed on the surface of the hydrogen storage alloy,which increases the specific surface area of the alloy.The discharge performance and cycle stability of the treated alloy were improved.The high rate discharge performance increases from 55.5% to 87.8%,32.3% higher.The median voltage increases from 1.210 V to 1.256 V,increased by 0.046 V.After 100 cycles the discharge capacity loss decreased from 37.5 mAh/g to 18.6 mAh/g.