▎ 摘　　要

NOVELTY - A hydrogel binder (10) comprises anionic polyacid, a cationic polyamine and a solvent. The anionic polyacid, a cationic polyamine are derived from an acid-base reaction between a polyacid and a polyamine in a weight ratio of 10:100-40:100. USE - Hydrogel binder used for preparing free-standing electrode for batteries (all claimed). Uses include but are not limited to electrochromic devices, sensors for organic and bio-organic materials, field effect transistors, printing plates, portable electronics, drones, satellites and electric vehicles. ADVANTAGE - The hydrogel binder has a solid structure that allows an effective dispersion of materials to make the free-standing electrode. The free-standing electrode eliminates the need for metallic current collectors when made into batteries. The hydrogel binder is prepared by a method without requiring special equipment or laborious techniques. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) synthesis of the hydrogel binder, which involves mixing a polyacid with polyamine in a solvent; (2) free-standing electrode, which comprises the hydrogel binder and carbon nanotubes (14); (3) preparation of free-standing electrode, which involves mixing the hydrogel binder and carbon nanotubes (14) in a mixing solvent to form a slurry, casting, and drying the slurry on a substrate; and (4) battery, which comprises the free-standing electrode, sulfur source, a separator and an electrolyte. DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of general procedure for preparing of free-standing electrodes used in lithium-ion batteries (LIB) or lithium sulfur batteries. Polyethyleneamine (2) Alginic acid (4) Hydrogel binder (10) Carbon nanotubes (14) Carbon fibers (16)