This application discloses a metal hydroxide, a positive electrode material, an electrochemical device, and an electrical device. The metal hydroxide includes Ni element. An axial lattice constant c Å of the metal hydroxide satisfies: 0.363x + 4.2 ≤ c ≤ 0.363x + 4.4, where, based on a total molar mass of a metal element in the metal hydroxide, a molar percentage of the Ni element in the metal hydroxide is x. The lattice constant c of the metal hydroxide falls within a specified value range. The positive electrode material prepared from the metal hydroxide serving as a precursor is of excellent structural stability in a charging and discharging environment, and improves the cycle performance, high-temperature performance, and safety performance of lithium-ion batteries.