Cover plate assembly, battery cell, battery module, battery pack, and apparatus

A cover plate assembly for a battery cell, wherein the cover plate assembly comprises:

• a top cover plate, wherein the top cover plate is provided with an explosion-proof valve;
• and
• an insulating plate, laminated with the top cover plate, wherein the insulating plate comprises a base portion and a thinned region located in the base portion, the thinned region is formed by thinning the base portion, and in a thickness direction of the cover plate assembly, a region enclosed by boundaries of an orthographic projection of the thinned region at least partially overlaps an orthographic projection of the explosion-proof valve;
• wherein the insulating plate comprises two surfaces disposed opposite each other in the thickness direction, and the thinned region comprises a groove formed by at least one of the two surfaces being recessed;
• the insulating plate comprises a recess portion, and the recess portion is formed by the base portion being recessed in a direction away from the top cover plate, and is disposed corresponding to the explosion-proof valve in the thickness direction;
• and
• the groove is disposed on the periphery of the recess portion, the thickness of the insulating plate at the thinned region is smaller than the thickness of the insulating plate at the recess portion.