A lithium ion battery, comprising: a cover plate assembly, comprising a pole and a polarity connecting piece, and the pole is connected with the polarity connecting piece; a battery cell assembly, provided with at least one battery cell tab assembly, and the pole is connected and conducted with the at least one battery cell tab assembly through the polarity connecting piece. a shell, and the battery cell assembly and the polarity connecting piece are disposed in the shell; a supporting part, disposed in the shell and configured to support the battery cell assembly, and the cover plate assembly is disposed at the opening of the shell and connected with the supporting part. wherein the polarity connecting piece comprises: a polarity plate body, a first through hole is formed in the polarity plate body, a first protrusion and a first folded edge are disposed on the side, facing the battery cell assembly, of the polarity plate body, a first groove is formed in the edge of the first folded edge, the first protrusion is connected with the supporting part, part of the pole penetrates through the cover plate assembly and extends into the shell to be in interference fit with the polarity plate body through the first through hole, and the groove wall of the first groove is connected with the battery cell tab assembly; wherein the supporting part comprises: two fixing frames, the two fixing frames are oppositely disposed and connected in a first direction; two protection plates, the two protection plates are oppositely arranged in a second direction, the two protection plates are located on two sides of the two fixing frames respectively, the two fixing frames and the two protection plates define an installation space, the battery cell assembly is located in the installation space, the battery cell assembly is provided with two battery cell tab assemblies, and the two battery cell tab assemblies are disposed facing a side where the protection plates are located; wherein one of the two fixing frames is provided with a locking column, the other fixing frame of the two fixing frames is provided with a connecting hole matched with the locking column, and/or, a first end of each fixing frame is provided with a locking column, and a second end of the each fixing frame is provided with a connecting hole. a cover plate assembly, comprising a pole and a polarity connecting piece, and the pole is connected with the polarity connecting piece; a battery cell assembly, provided with at least one battery cell tab assembly, and the pole is connected and conducted with the at least one battery cell tab assembly through the polarity connecting piece. a shell, and the battery cell assembly and the polarity connecting piece are disposed in the shell; a supporting part, disposed in the shell and configured to support the battery cell assembly, and the cover plate assembly is disposed at the opening of the shell and connected with the supporting part. a polarity plate body, a first through hole is formed in the polarity plate body, a first protrusion and a first folded edge are disposed on the side, facing the battery cell assembly, of the polarity plate body, a first groove is formed in the edge of the first folded edge, the first protrusion is connected with the supporting part, part of the pole penetrates through the cover plate assembly and extends into the shell to be in interference fit with the polarity plate body through the first through hole, and the groove wall of the first groove is connected with the battery cell tab assembly; wherein the supporting part comprises: two fixing frames, the two fixing frames are oppositely disposed and connected in a first direction; two protection plates, the two protection plates are oppositely arranged in a second direction, the two protection plates are located on two sides of the two fixing frames respectively, the two fixing frames and the two protection plates define an installation space, the battery cell assembly is located in the installation space, the battery cell assembly is provided with two battery cell tab assemblies, and the two battery cell tab assemblies are disposed facing a side where the protection plates are located; wherein one of the two fixing frames is provided with a locking column, the other fixing frame of the two fixing frames is provided with a connecting hole matched with the locking column, and/or, a first end of each fixing frame is provided with a locking column, and a second end of the each fixing frame is provided with a connecting hole. two fixing frames, the two fixing frames are oppositely disposed and connected in a first direction; two protection plates, the two protection plates are oppositely arranged in a second direction, the two protection plates are located on two sides of the two fixing frames respectively, the two fixing frames and the two protection plates define an installation space, the battery cell assembly is located in the installation space, the battery cell assembly is provided with two battery cell tab assemblies, and the two battery cell tab assemblies are disposed facing a side where the protection plates are located; wherein one of the two fixing frames is provided with a locking column, the other fixing frame of the two fixing frames is provided with a connecting hole matched with the locking column, and/or, a first end of each fixing frame is provided with a locking column, and a second end of the each fixing frame is provided with a connecting hole.