A lithium ion battery includes a front cover (1), a circuit board (3), a polymer cell (4), a rear cover (7) and a metal foil (6). The front cover (1) is provided with a snap and the circuit board (3) is fixedly connected to the front cover (1) by the snap; and the circuit board (3) is fixedly connected to an output end of the polymer cell (4) by spot welding. The circuit board (3) is electrically connected to the polymer cell (4) by a pole piece and the bottom of the polymer cell (4) is fixedly connected to the rear cover (7) by a hot melt adhesive (2); and side walls of the polymer cell (4) are coated with the metal foil (6).
