Battery, battery pack, electronic apparatus, electrically driven vehicle, electrical storage device, and power system

A battery, comprising:

• a positive electrode that includes a positive electrode current collector, and a positive electrode active material layer which includes a positive electrode active material and is provided on both surfaces of the positive electrode current collector;
• a negative electrode;
• a separator that includes at least a porous film;
• and
• an electrolyte,
• wherein the positive electrode active material includes a positive electrode material including a lithium cobalt composite oxide which has a layered structure and includes at least lithium and cobalt,
• an area density S (mg/cm2) of the positive electrode active material layer is 27 mg/cm2 or greater, and the porous film satisfies the following Expressions.
• 0.04≦Ri≦−0.07L−0.09×S+4.99
• Ri=τ2L/ε′
• ε′=[{(L×ε/100)−Rz×0.46/3}/L]×100
• τ={(1.216×ε′Td×10−4)/L}0.5 (Expressions)
• [provided that, Ri:
• a film resistance (μm), L:
• a film thickness (μm), τ:
• a tortuosity factor, T:
• air permeability (sec/100 cc), d:
• a pore size (nm), Rz:
• a surface roughness maximum height (the sum of values of a front surface and a rear surface) (μm), ε:
• porosity (%), ε′:
• corrected porosity (%), and S:
• the area density of the positive electrode active material layer (mg/cm2)]