Structure and lithium storage performances of nickel hydroxides synthesized with different nickel salts

Nickel hydroxides with hierarchical micro-nano structures are prepared by a facile homogeneous precipitation method with different nickel salts (Ni(NO3)(2)center dot 6H(2)O, NiCl2 center dot 6H(2)O, and NiSO4 center dot 6H(2)O) as raw materials. The effect of nickel sources on the microstructure and lithium storage performance of the nickel hydroxides is studied. It is found that all the three prepared samples are alpha-nickel hydroxide. The nickel hydroxides synthesized with Ni(NO3)(2)center dot 6H(2) or NiCl2 center dot 6H(2)O show a similar particle size of 20-30 mu m and are composed of very thin nano-sheets, while the nickel hydroxide synthesized with Ni(SO4)(2)center dot 6H(2)O shows a larger particle size (30-50 mu m) and consists of very thin nano-walls. When applied as anode materials for lithium-ion batteries (LIBs), the nickel hydroxide synthesized with NiSO4 center dot 6H(2)O exhibits the highest discharge capacity, but its cyclic stability is very poor. The nickel hydroxides synthesized with NiCl2 center dot 6H(2)O exhibit higher discharge capacity than the nickel hydroxides synthesized with Ni(NO3)(2)center dot 6H(2)O, and both of them show much improved cyclic stability and rate capability as compared to the nickel hydroxide synthesized with Ni(SO4)(2)center dot 6H(2)O. Moreover, pseudocapacitive behavior makes a great contribution to the electrochemical energy storage of the three samples. The discrepancies of lithium storage performance of the three samples are analyzed by ex-situ XRD, FT-IR, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests.