A transition metal hydroxy-anion electrode material for lithium-ion battery cathodes includes the charge-neutral structure Mx(OH)n(XO4)m, where M is one or more transition metals, x is the total number of transition metal atoms, X is sulfur or phosphorus, and x, n, and m are integers. The polyanion material has a nanostructured morphology. (OH)n(XO4)m is a hydroxysulfate or hydroxyphosphate, and M can be one or more (e.g., a solid solution of) transition metals selected from the group consisting of copper, iron, manganese, nickel, vanadium, cobalt, zinc, chromium, and molybdenum. A lithium-ion battery may have a cathode including Mx(OH)n(XO4)m as a cathode material, and an electronic device may include a lithium-ion battery having a cathode including Mx(OH)n(XO4)m as a cathode material.