Battery armoring stainless steel foil, and method of producing same
Provided is a battery armoring stainless steel foil which, without the need for a special treatment such as corona discharge, has excellent adhesiveness to resin after being thermally shocked and after being immersed in an electrolyte solution. A battery armoring stainless steel foil ( 1 ) includes an oxide film ( 1 a ), having a thickness of not less than 2 nm, which contains (i) one or more metallic elements, existing as a hydroxide, in an amount of not less than 35 mol percent and (ii) SiO 2 in an amount of not more than 40 mol percent, the battery armoring stainless steel foil ( 1 ) having an arithmetic mean roughness Ra of less than 0.1 μm but not less than 0.02 μm in a direction orthogonal to a direction in which the battery armoring stainless steel foil ( 1 ) has been rolled.
1. A battery armoring stainless steel foil comprising:
a stainless steel foil as a base material,
an oxide film, having a thickness of not less than 2 nm and not more than 5 nm, which contains (i) Fe and Cr, each existing as a hydroxide, in a combined amount of not less than 35 mol percent and (ii) SiO 2 in an amount of more than 0 mol percent and not more than 40 mol percent,
the oxide film containing oxides of Fe and Cr,
the oxide film being formed, on a surface of the stainless steel foil, as a single layer in which Fe content is larger than Cr content, and
the battery armoring stainless steel foil having an arithmetic mean roughness Ra of less than 0.1 μm but not less than 0.02 μm in a direction orthogonal to a direction in which the battery armoring stainless steel foil has been rolled.
2. The battery armoring stainless steel foil of claim 1 , wherein the battery armoring stainless steel foil has a thickness of not less than 5 μm and not more than 100 μm.
3. The battery armoring stainless steel foil of claim 1 , wherein the surface of the stainless steel foil as the base material and a surface of the oxide film has an arithmetic mean roughness Ra of not less than 0.02 μm and less than 0.1 μm in the direction orthogonal to the direction in which the battery armoring stainless steel foil has been rolled.
4. The battery armoring stainless steel foil of claim 1 , wherein the oxide film is formed on the surface of the stainless steel foil by annealing the stainless steel foil as the base material.
5. A method of producing a battery armoring stainless steel foil recited in claim 1 , the method comprising the steps of:
obtaining a rolled stainless steel foil which has an arithmetic mean roughness Ra of less than 0.1 μm but not less than 0.02 μm in a direction orthogonal to a direction in which the rolled stainless steel foil has been rolled; and
forming an oxide film by annealing the rolled stainless steel foil at a temperature in a range of 900° C. to 1180° C. in a reducing atmosphere in which (i) a dew point falls in the range of −40° C. to −60° C. and (ii) a hydrogen partial pressure is not less than 75%.