Anion exchange membranes (AEMs) with excellent stability and high ion conductivity are fabricated via the formation of internal cross linking networks. The internal crosslinking networks are constructed by reacting 4,4'-bipyridine with chloromethylated polysulfone. The bipyridine group simultaneously functions as ionic conductor and cross linker in this system. The performance of the membrane is tuned via controlling the 4,4'-bipyridine content in the casting solution. The prepared membranes demonstrate excellent chemical stability and high ion conductivity under acidic conditions. As a consequence, the membranes show very promising performance for vanadium flow battery application, exhibiting a Coulombic efficiency of 99.2% and an energy efficiency of 81.8% at a current density of 140 mA cm(-2). The battery that is assembled with the prepared membrane shows a stable battery performance over more than 1600 cycles, which is by far the longest cycle life reported. These results indicate that the AEMs with internal crosslinking structures are promising candidates for battery systems and even for fuel cells.