Patent ID: 8614019

Claim:
An electricity storage device comprising: a positive electrode current collector; a positive electrode disposed on said positive electrode current collector, including a positive electrode active material capable of reversibly absorbing and desorbing at least anions; a negative electrode current collector; and a negative electrode disposed on said negative electrode current collector, comprising a negative electrode active material substantially capable of reversibly absorbing and desorbing lithium ions; wherein: said negative electrode active material is at least one selected from the group consisting of silicon, a silicon-containing alloy, a silicon compound, tin, a tin-containing alloy, and a tin compound; lithium in an amount corresponding to an irreversible capacity of said negative electrode active material and corresponding to 20 to 95% of reversible capacity of said negative electrode active material is absorbed in said negative electrode, when said electricity storage device is in a completely discharged state; and said negative electrode is a thin film having a thickness of 10 μm or less.