Preparation And Electrochemical Properties Of The New Type Of Ni (oh) X Electrode Materials

The positive active materials Ni(OH)_x for Ni-based rechargeable alkaline batteries were prepared through a simple route of chemical oxidation. FT-IR, XRD, SEM, TEM and TG/DSC were taken to characterize the samples; Average Ni oxidation state(OS) of the sample and the electrochemical performance were investigated, respectively. Results show that a core/shell structure is formed with theβ-NiOOH coating outside after surface modification. OS of the different samples are between 2.01 and 2.42 with the Ni³⁺/T_Ni values (in mol) in 1%～42%. The Ni/MH battery models with the above treated samples as positive materials show considerable electrochemical performance with the discharge capacity of 275±10 mAh·g^-1 under 0.2 C, also, a good electrochemical performance is observed at high discharge density with a capacity maintenance above 98% after nearly 300 cycles under 1C charge/discharge rate.Investigations inviting many methods show that the nickel electrode after modification exhibits a smaller value ofΔE_a,c and charge transfer resistance, which suggest a better activity and reversibility of redox reaction. Besides, the charge/discharge tests under different cut voltages indicate that the modified electrode shows an unconspicuous second discharge plateau compared with the untreated one, which results in a comparable capacity about 302 mAh·g^-1 between the modified electrode at the first discharge plateau and the primary electrode at a deeper cut voltage.Again, two sequential stages occur through the discharging process according to the EIS testing. For the first, is the stage before the completely covering of Ni(OH)₂, and the second is the stage for further reaction to the inside of electrode after a whole covering of Ni(OH)₂ on the surface. The second stage for the modified electrode is delayed compared with the untreated electrode which can be attributed to the amorphous structure of coating favoring to the proton diffusing process during deoxidation. Thus, the kinectics characteristics of nickel electrode is improvedTests at high-temperature indicate that the discharge capacity for the NiOOH coated electrode is 50 mAh·g^-1 larger than the Co-coated one at 60℃. And the oxidative modification for nickel electrode does not play a part in increasing the over potential of oxygen evolution but in leaving it happen which will absolutely improve the charge efficiency. CV tests under different temperatures indicate that the oxidation modified nickel electrode stabilizes the deoxidation potential which results in an improvement of redox reversibility.