NOVELTY - Solid electrolyte (120) comprises: interpenetrating polymer network comprising ethylene oxy segments (I), and formed by polymerizing a first substituted ethylene oxy monomer (II), with a second substituted ethylene oxy monomer (III) under an initiator; a plasticizer dispersed in the interpenetrating polymer network; and a lithium salt dispersed in the interpenetrating polymer network, where a molecular weight of the first monomer or the second monomer is 100-800, the first monomer is less than or equal to 50 wt.% of the second monomer, and the lithium salt is less than or equal to 10 wt.% of the second monomer.    USE - The solid electrolyte is useful in a lithium based battery which is a lithium metal battery or a lithium ion battery (all claimed).    ADVANTAGE - The solid electrolyte: utilizes the interpenetrating polymer network having deceased crosslinking degree and crystallization and improved mobility of the branched chains of the interpenetrating polymer network, and which has good thermal stability and electro-chemical stability; has good thermal stability and electro-chemical stability; has improved ionic conductivity even under a room temperature or if lithium perchlorate is low in content; utilizes the plasticizer which acts as a flame retardant to prevent the solid electrolyte from being burned; and provides long life span, high power, good stability and safety for lithium based battery.    DETAILED DESCRIPTION - Solid electrolyte (120) comprises: interpenetrating polymer network comprising ethylene oxy segments of formula (-(CH2-CH2-O-)n-) (I), and formed by polymerizing a first substituted ethylene oxy monomer of formula (R1-O-(CH2-CH2-O-)n-R2) (II), with a second substituted ethylene oxy monomer of formula (R3-O-(CH2-CH2-O-)m-R4) (III) under an initiator; a plasticizer dispersed in the interpenetrating polymer network; and a lithium salt dispersed in the interpenetrating polymer network, where a molecular weight of the first monomer or the second monomer is 100-800, the first monomer is less than or equal to 50 wt.% of the second monomer, and the lithium salt is less than or equal to 10 wt.% of the second monomer.    R1-R3 = -C=C- or -CC- groups, preferably -CH=CH2, -CCH, -CH=CH-CH3, -(CH3)C=CH2, -CC-CH3 or -C(=O)-CH=CH2;    R4 = alkyl or H; and    m, n = integers.    An INDEPENDENT CLAIM is also included for a lithium based battery (100), comprising an anode (110), a cathode (130) and the solid electrolyte located between the anode and the cathode.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the lithium based battery.    Lithium based battery (100)    Anode (110)    Solid electrolyte (120)    Cathode (130)