NOVELTY - A lithium ion battery exterior material (1) comprises base material layer (11) which consists of nylon films, 1st contact bonding layer (12), metal foil layer (13), corrosion-prevention process layer (14), 2nd contact bonding layer (15), sealant layer (16) which is provided on opposite side to corrosion-prevention process layer of 2nd contact bonding layer, and base-material protective layer (18) which is provided in 2nd surface side of base material layer and contains water soluble polysaccharide (A), water-soluble polymer (B), plasticizer (C) and surfactant (D).    USE - An exterior material for lithium ion battery (claimed).    ADVANTAGE - Material has sufficient abrasion resistance and electrolyte solution tolerance. Adhesiveness, ductility and moldability are outstanding.    DETAILED DESCRIPTION - A lithium ion battery exterior material (1) comprises base material layer (11) which consists of nylon films, 1st contact bonding layer (12) which is provided in 1st surface side of base material layer, metal foil layer (13) which is provided on opposite side to base material layer of 1st contact bonding layer, corrosion-prevention process layer (14) which is provided on opposite side to 1st contact bonding layer of metal foil layer, 2nd contact bonding layer (15) which is provided on opposite side to metal foil layer of corrosion-prevention process layer, sealant layer (16) which is provided on opposite side to corrosion-prevention process layer of 2nd contact bonding layer, 3rd contact bonding layer which is provided in 2nd surface side of base material layer, and base-material protective layer (18) which is provided in 2nd surface side of base material layer and contains water soluble polysaccharide (A), water-soluble polymer (B), plasticizer (C) and surfactant (D). Amount of water soluble polysaccharide dissolved in 100 mass parts solvent chosen from 50 mass% alcohol aqueous solution containing methanol, ethanol, propanol or isopropyl alcohol and water is greater than or equal to 1 mass part. Water-soluble polymer (B) has molecular weight of greater than or equal to 10000 and greater than or equal to 1 mass part is dissolved in 100 mass parts solvent chosen from 50 mass% alcohol aqueous solution containing methanol, ethanol, propanol or isopropyl alcohol and water.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the lithium ion battery exterior material.    Lithium ion battery exterior material (1)    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)    Base-material protective layer (18)