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, the area density S (mg/cm 2 ) of the positive electrode active material layer is 27 mg/cm 2 or greater, and the porous film satisfies the following Expressions: 0.04 ≤ Ri ≤ − 0.07 ⁢ L − 0.09 × S + 4.99 Ri = τ 2 L / ε ′ ε ′ = L × ε/ 100 − Rz × 0.46 / 3 / L × 100 τ = 1.216 × ε ′ Td × 10 − 4 / L 0.5 wherein Ri: the film resistance (μm), L: the film thickness (μm), τ: the tortuosity factor, T: air permeability (sec/100 cc), d: the pore size (nm), Rz: the 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/cm 2 ) whereby the pore size d is an average pore size measured by the non-mercury Palm Polo meter, the surface roughness maximum height Rz is measured in accordance with JIS B601 by using the nanoscale hybrid microscope, the porosity is measured by a gravimetric method, the air permeability is a Gurley air permeability measured in accordance with JIS P8117 and the film thickness L is an average film thickness measured by the probe type film thickness meter Digital Guagestand. 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, the area density S (mg/cm 2 ) of the positive electrode active material layer is 27 mg/cm 2 or greater, and the porous film satisfies the following Expressions: 0.04 ≤ Ri ≤ − 0.07 ⁢ L − 0.09 × S + 4.99 Ri = τ 2 L / ε ′ ε ′ = L × ε/ 100 − Rz × 0.46 / 3 / L × 100 τ = 1.216 × ε ′ Td × 10 − 4 / L 0.5 wherein Ri: the film resistance (μm), L: the film thickness (μm), τ: the tortuosity factor, T: air permeability (sec/100 cc), d: the pore size (nm), Rz: the 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/cm 2 ) whereby the pore size d is an average pore size measured by the non-mercury Palm Polo meter, the surface roughness maximum height Rz is measured in accordance with JIS B601 by using the nanoscale hybrid microscope, the porosity is measured by a gravimetric method, the air permeability is a Gurley air permeability measured in accordance with JIS P8117 and the film thickness L is an average film thickness measured by the probe type film thickness meter Digital Guagestand. <EOS>