As a specific example, the active material bulk may be a sintered body in which the electrode active material particles of the raw material are bound to each other while forming a neck. FIG. 3 is drawing illustrating active material particles 210 which are bound to each other by the neck (indicated by an arrow in FIG. 3), based on the two electrode active material particles 110 adjacent to each other in the raw material. As is known, the sintering process is divided into an initial stage, a middle stage, and a terminal state, and in the initial sintering stage, a neck is formed between the particles. Though it depends somewhat on the kind and content of additive included in the raw material, the initial sintering stage may correspond to a stage in which a sintering shrinkage is about 3 to 10% (vol %), specifically reaches 3 to 7%. In the initial sintering stage, most pores in the molded body are substantially present as open pores, mostly mass transfer (diffusion) occurs by a contact point of particles, and particles are connected by a neck. Accordingly, when the sintered body is a product in the initial sintering stage of forming an interparticle neck of an electrode active material, the sintered body may contain large amount of open pores while having mechanical (physical) strength capable of stable handling during processes such as cutting, transfer, and adhesion and process performance, and thus, very advantageous in terms of electrolyte solution impregnation and electrochemical reaction area improvement. In addition, even though the cut film is in the form of a thick film, may have a structure in which a large amount of open pore channels penetrate the cut film regardless of the cutting direction, and thus, the electrolyte solution may permeate uniformly in the thickness direction of the cut film.
