Patent ID: 8722245

Claim:
A secondary battery comprising: a cathode; an anode; and an electrolyte, wherein, the anode comprises an anode current collector and an anode active material layer containing silicon (Si) as an element on the anode current collector, the anode active material layer has a plurality of primary particles grown in one layer on the anode current collector and in contact with the anode current collector, at least some of the plurality of primary particles are adjacent and joined to each other along a direction parallel to a surface of the anode current collector and aggregate to form a secondary particle, said anode active material layer has a plurality of distinct secondary particles, respective grooves are formed between adjacent secondary particles separating the adjacent secondary particles from each other, each groove being wider at an opening of the groove than at a bottom of the groove, the bottom of the groove comprising a surface of the anode active material layer, each secondary particle comprises more than two primary particles that are joined and curved in an identical direction with respect to each other when viewed in cross section of the secondary battery along a thickness direction of the anode current collector, the anode has a region including at least one groove and at least one set of adjacent secondary particles, and the anode active material layer is in contact with an entire surface of the anode current collector throughout the entire region.