ELECTRICITY STORAGE ELEMENT

PROBLEM TO BE SOLVED: To provide an electricity storage element capable of suppressing a decrease in output even after a long-term of neglect.SOLUTION: An electricity storage element includes a negative electrode having an active material layer. The active material layer contains particle-like non-graphitizable carbon, as an active material. Pores are formed between the non-graphitizable carbon, in the active material layer. The average particle diameter D50 of the non-graphitizable carbon is 2-10 μm. When the average particle diameter D50 is denoted as x μm and the porosity of the active material layer is denoted as y%, x and y satisfy a relational expression: y≤0.77x+33.23.SELECTED DRAWING: None 【課題】長期間放置された後でも出力が低下することを抑制された蓄電素子の提供。【解決手段】活物質層を有する負極を備え、活物質層は、粒子状の難黒鉛化炭素を活物質として含み、活物質層には、難黒鉛化炭素の間に空孔が形成され、難黒鉛化炭素の平均粒径Ｄ５０は、２〜１０μｍであり、平均粒径Ｄ５０をｘμｍとし、活物質層の空孔率をｙ％としたときに、ｘ及びｙは、ｙ≦０．７７ｘ＋３３．２３の関係式を満たす、蓄電素子。【選択図】なし