 A sulfur cathode with enhanced electrochemical properties is prepared by a hydrogel binder owning three-dimensional polymeric network for Li–S batteries. The promising high-performance binder (Alg-Ca2+) is constructed by an in situ interconnection of alginate chains by additive divalent cation with a facile and self-assembly strategy. With the assistance of 3D network, the sulfur/activated carbon composite cathode exhibits a higher rate capability and cycling performance compared to poly(vinylidene fluoride) binder, and the capacity retention is up to 80.6 % after 200 cycles (0.5C, 1C = 1675 mA g−1). Additionally, the electrochemical impedance spectroscopy also reveals a lower electrode resistance and better kinetic characteristics with Alg-Ca2+ as a binder. The improved electrochemical behaviors are assigned to the ability of maintaining the electrode stability due to the excellent mechanical property and amorphous structure.