A method of joining a substrate for a bipolar electrode of a bipolar battery to a frame for supporting the bipolar electrode for use in the bipolar battery includes the implanting of a thermoplastic material in the substrate. The substrate and the frame are then vibration welded together at a frequency in the range of 50 Hz to 1 kHz to melt the thermoplastic material. The melted thermoplastic material forms a continuous or substantially continuous loop around the substrate to join the substrate and the frame together. A bipolar battery comprising a substrate and a frame joined together by the method, and a substrate for a bipolar electrode for use in the method are also described.