Comparative study on microstructure of β-Ni(OH)_(2) as cathode material for Ni-MH battery

Microstructures such as micro-strain,crystallite as well as stacking faults can result in broadening of X-ray diffraction lines.Based on least square principle,new com-putation method and programs,which can separate the two-fold broadening effect caused by crystallite/stacking faults and which can separate the three-fold broadening effect caused by crystallite/residual stress/stacking faults,have been proposed.As a result,mi-cro-strain and crystallite sizes as well as stacking fault probability can be calculated re-spectively and investigated in detail.Then the microstructures ofβ-Ni(OH)_(2)are investi-gated by means of these methods.The main results are as follows:1)The shape and size of crystallite as well as stacking fault probability of rawβ-Ni(OH)_(2)are dependent on its preparation technique.2)Activation changes the microstructure ofβ-Ni(OH)_(2).It transforms the crystallite shape from short-fat cylinder into polyhedrons or nearly equiaxial grains.Activation also alters the residual strain states and stacking fault probability.3)After charge-discharge and cycle-lifetime testing,the crystallites ofβ-Ni(OH)_(2)are fined further and its residual strain and fault probability were alternated.The extent of these effects are dependent on circulating conditions.4)Calcium additive inβ-Ni(OH)_(2)restrains grain fining process and turns twin fault into deformation fault.5)Comprehensive analysis reveals that micro structural parameters ofβ-Ni(OH)_(2)are correlated with some performance of Ni-MH battery.

Novel hierarchical yolk-shell α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres as high specific capacitance electrode materials for supercapacitors

For high performance supercapacitors, novel hierarchical yolk-shell α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres were controllably synthesized using a facile two-step method based on the solvothermal treatment. The unique α-Ni(OH)_(2) based yolk-shell microstructures decorated with numerous interconnected nanosheets and the heterocomposition features can synergistically enhance reactive site exposure and electron conduction within the microspheres, facilitate charge transfer between electrolyte and electrode materials, and release structural stress during OH− chemisorption/desorption. Moreover, the Mn2O3 sediments distributed over the α-Ni(OH)_(2) microspheres can serve as an effective protective layer for electrochemical reactions. Consequently, when tested in 1 mol·L^(−1) KOH aqueous electrolyte for supercapacitors, the yolk-shell α-Ni (OH)_(2)/Mn_(2)O_(3) microspheres exhibited a considerably high specific capacitance of 2228.6 F·g^(−1) at 1 A·g^(−1) and an impressive capacitance retention of 77.7% after 3000 cycles at 10 A·g^(−1). The proposed α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres with hetero-composition and unique hierarchical yolk-shell microstructures are highly promising to be used as electrode materials in supercapacitors and other energy storage devices.