Lithium ion secondary battery

A lithium ion secondary battery, comprising:

• a cathode;
• an anode;
• a separator;
• and
• an electrolyte comprising an ionic liquid and a lithium salt,
• wherein the separator has a porosity of from 80% to 98%, and
• at least one of the following conditions (1) or (2) is fulfilled:
• (1) the cathode comprises a first current collector and a cathode mixture applied onto at least one side of the first current collector, wherein an amount of the cathode mixture applied onto the one side of the first current collector is from 1 mg/cm2 to 10 mg/cm2 and a volume porosity of the cathode mixture is from 20% by volume to 45% by volume;
• and
• (2) the anode comprises a second current collector and an anode mixture applied onto at least one side of the second current collector, wherein an amount of the anode mixture applied onto the one side of the second current collector is from 1 mg/cm2 to 10 mg/cm2 and a volume porosity of the cathode mixture is from 20% by volume to 45% by volume.