Advances in Nickel Hydroxide: Structures and Modern Applications (review)

This review article provides an overview of research conducted over the past few decades on nickel hydroxide, a crucial material in both physics and chemistry with notable engineering applications, particularly in batteries. It begins by outlining the structures of the two known polymorphs, α-Ni(OH)2 and β-Ni(OH)2. The article also explores various types of disorder commonly found in nickel hydroxide, such as hydration, stacking faults, mechanical stresses, and the incorporation of ionic impurities. Related materials, including intercalated α-derivatives and basic nickel salts, are also discussed. The review goes on to summarize several methods for synthesizing nickel hydroxide, such as chemical and electrochemical precipitation, sol–gel synthesis, chemical aging, hydrothermal and solvothermal synthesis, electrochemical oxidation, microwave-assisted synthesis, and sonochemical methods. Finally, the known physical properties of nickel hydroxide—magnetic, vibrational, optical, electrical, and mechanical—are examined. The concluding section offers a summary of the potentially valuable properties of these materials and techniques for identifying and characterizing unknown nickel hydroxide-based samples.