An in-vehicle lithium ion battery member produced by molding a resin composition containing (a) a polyphenylene ether resin, the resin composition having a critical strain in a chemical resistance evaluation, determined as described in " Chemical resistance" in the description, of 0.5% or more and a Charpy impact strength at 23 °C, determined as described in " Impact resistance" in the description, of 20 kJ/m 2 or more, wherein the resin composition for the in-vehicle lithium ion battery member contains (c) an olefinic polymer constituted from an olefin, a sea-island phase structure having a sea phase containing the (a) component and island phases containing the (c) component and present in the sea phase is formed in a morphology image of the in-vehicle lithium ion battery member, and in a second processed image obtained through a binarization of the morphology image, determined as described in " Morphology" in the description, a number per unit area of second black portions that are black after the binarization and have an area of 4.92 × 10 -4 μm 2 or more is 8/μm 2 or more, and in a case where AW2 (μm 2 /μm 2) represents an occupied area per unit area by second white portions that are white after the binarization, and L2 (μm/μm 2) represents a length per unit area of a total peripheral length which is a sum of peripheral lengths of second non-small portions having an area of 15 × 10 -4 μm 2 or more among the second black portions, the length L2 relative to the occupied area AW2 (L2/AW2) is 7 μm -1 or more. the resin composition having a critical strain in a chemical resistance evaluation, determined as described in " Chemical resistance" in the description, of 0.5% or more and a Charpy impact strength at 23 °C, determined as described in " Impact resistance" in the description, of 20 kJ/m 2 or more, wherein the resin composition for the in-vehicle lithium ion battery member contains (c) an olefinic polymer constituted from an olefin, a sea-island phase structure having a sea phase containing the (a) component and island phases containing the (c) component and present in the sea phase is formed in a morphology image of the in-vehicle lithium ion battery member, and in a second processed image obtained through a binarization of the morphology image, determined as described in " Morphology" in the description, a number per unit area of second black portions that are black after the binarization and have an area of 4.92 × 10 -4 μm 2 or more is 8/μm 2 or more, and in a case where AW2 (μm 2 /μm 2) represents an occupied area per unit area by second white portions that are white after the binarization, and L2 (μm/μm 2) represents a length per unit area of a total peripheral length which is a sum of peripheral lengths of second non-small portions having an area of 15 × 10 -4 μm 2 or more among the second black portions, the length L2 relative to the occupied area AW2 (L2/AW2) is 7 μm -1 or more. a number per unit area of second black portions that are black after the binarization and have an area of 4.92 × 10 -4 μm 2 or more is 8/μm 2 or more, and in a case where AW2 (μm 2 /μm 2) represents an occupied area per unit area by second white portions that are white after the binarization, and L2 (μm/μm 2) represents a length per unit area of a total peripheral length which is a sum of peripheral lengths of second non-small portions having an area of 15 × 10 -4 μm 2 or more among the second black portions, the length L2 relative to the occupied area AW2 (L2/AW2) is 7 μm -1 or more.