| CPC C23C 28/02 (2013.01) [B32B 15/011 (2013.01); C23C 28/021 (2013.01); C25D 5/12 (2013.01); C25D 5/50 (2013.01); C25D 5/605 (2020.08); H01M 50/119 (2021.01); H01M 50/1243 (2021.01); H01M 50/128 (2021.01); H01M 50/182 (2021.01)] | 7 Claims |

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1. A surface-treated steel sheet, comprising:
a steel sheet; and
a nickel-cobalt-iron diffusion layer formed as an outermost surface layer on the steel sheet,
wherein when a content of Ni, a content of Co and a content of Fe of the nickel-cobalt-iron diffusion layer are determined based on a Ni intensity, a Co intensity and a Fe intensity each sequentially measured in the depth direction from the surface side of the nickel-cobalt-iron diffusion layer by a radio frequency glow discharge optical emission spectrometry, a content of Co at a specific depth position D, InCo_D, is 8.59% by mass or higher and 65% by mass or lower, a content of Fe at the specific depth position D, InFe_D, is 18% by mass or higher and 70% by mass or lower, a content of Ni at the specific depth position D, InNi_D is 5% by mass or higher and 34.55% by mass or lower, the specific depth position D being a position where the Ni intensity is 0.5% of the maximum value of the Ni intensity, and
wherein the total content of nickel and cobalt in the nickel-cobalt-iron diffusion layer is 9.0 g/m2 or lower.
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