Secondary battery

1 . A secondary battery, comprising:

a positive electrode including

a positive electrode core,

a positive electrode mixture layer provided on the positive electrode core, and

a surface layer constituting an outermost surface layer of the positive electrode, the surface layer being in direct contact with the positive electrode mixture layer at a position opposite to the positive electrode core across the positive electrode mixture layer and covers an entire outer surface of the positive electrode mixture layer, the surface layer containing an inorganic compound;

a negative electrode; and

a separator located between the positive electrode and the negative electrode, wherein

a first thickness variation coefficient of the positive electrode mixture layer is 0.01 to 0.30, where the first thickness variation coefficient is a ratio of a standard deviation to a mean of a thickness of the positive electrode mixture layer,

a packing density of an active material in the positive electrode mixture layer is 3.2 g/cm 3 or higher, and

a second thickness variation coefficient of the surface layer is 0.51 or greater, where the second thickness variation coefficient is a ratio of a standard deviation to a mean of a thickness of the surface layer.

2 . The secondary battery according to claim 1 , wherein

the average thickness of the surface layer is 0.1 μm to 10 μm.

3 . The secondary battery according to claim 1 , wherein the inorganic compound is at least one of an oxide, hydroxide, oxyhydroxide, borate, phosphate, and sulfate that contains at least one metal element selected from Al, Sn, W, Nb, Mo, Si, and Ba.

4 . The secondary battery according to claim 1 , wherein a porosity of the surface layer is 25% to 55%.

5 . The secondary battery according to claim 1 , wherein a volume-based median diameter of the inorganic compound is 0.05 μm to 1 μm.