NOVELTY - A lithium ion battery exterior material comprises base material layer (11), 1st contact bonding layer (12) on 1st surface side of base material layer, metal foil layer (13) on other side of base material layer of 1st contact bonding layer, corrosion-prevention process layer (14) on opposite side to 1st contact bonding layer of metal foil layer, 2nd contact bonding layer (15) on opposite side to metal foil layer of corrosion-prevention process layer, sealant layer (16) on other side of corrosion-prevention process layer of 2nd contact bonding layer, and 3rd contact bonding layer (17).    USE - A lithium ion battery exterior material for lithium ion battery used for video camera, satellite, submarine, electric vehicle, and electric-power-assisted bicycle.    ADVANTAGE - The lithium ion battery exterior material has sufficient moldability and electrolyte solution tolerance and excellent abrasion resistance and water resistance.    DETAILED DESCRIPTION - A lithium ion battery exterior material comprises base material layer (11), 1st contact bonding layer (12) on 1st surface side of base material layer, metal foil layer (13) on other side of base material layer of 1st contact bonding layer, corrosion-prevention process layer (14) on opposite side to 1st contact bonding layer of metal foil layer, 2nd contact bonding layer (15) on opposite side to metal foil layer of corrosion-prevention process layer, sealant layer (16) on other side of corrosion-prevention process layer of 2nd contact bonding layer, 3rd contact bonding layer (17) on 2nd surface side of base material layer, and base-material protective layer ( alpha ) (18) on opposite side to base material layer of 3rd contact bonding layer or base-material protective layer ( beta ) which makes 1 layer the 3rd contact bonding layer and the base-material protective layer. The base-material protective layer contains water-soluble polysaccharide (A) and additive (B). At 85 degrees C, greater than or equal to 1 mass% of component (A) dissolves in 100 mass% of alcohol aqueous solution containing 50 mass% of methanol, ethanol, propanol, or isopropanol, and component (B) contains hydroxyl (OH) group and a substance for crosslinking-reaction.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional diagram of a lithium ion battery exterior material consisting of protective layer, 3rd contact bonding layer, and base-material protective layer (alpha).    Base material layer (11)    1st contact bonding layer (12)    Metal foil layer (13)    Corrosion-prevention process layer (14)    2nd contact bonding layer (15)    Sealant layer (16)    3rd contact bonding layer (17)    Base-material protective layer alpha (18)