TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Salt: The lithium salt exists in the form of solid microparticles and is densely dispersed in the solid medium. Alternately, the lithium salt has composition represented by formula: Li+(M(SX)4)-.M=boron or aluminum;andX=fluorine atom or cyano group substituted 1-12C aliphatic group, 6-12C aromatic group, 6-12C aromatic group substituted 1-6C alkyl, preferably pentafluorophenyl group.    TECHNOLOGY FOCUS - POLYMERS - Preferred Medium: The solid medium is a polymer chosen from polyethylene oxide, ethylene oxide-propylene oxide copolymer, polyethylene glycol dimethyl ether, poly(methoxy) oligoethylene glycoxy)methacrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyvinylidene fluoride and vinylidene-fluoride-hexafluoropropylene copolymer. The solid medium further includes a plasticizer chosen from 12-crown-4,15-crown-5,18-crown-6, ethylene carbonate, propylene carbonate, diethyl carbonate and (gamma)-butyrolactone. Preferred Definitions:    Q=organic ligand having coordinating nitrogen atom or coordinating oxygen atom;    n=0 or 1;    M=boron;and    X=aliphatic group having electron-attractive group as substituent, aromatic group or aromatic-group substituted alkyl, where the substituent is fluorine atom or cyano group.    EXAMPLE - Pentafluorothiol (in g) (10.25) was dissolved in tetrahydrofuran (30 ml), to obtain a solution. Tetrahydrofuran solution of lithium borohydrate (6.4 ml) was slowly dripped into the solution, and heat-refluxed for 24 hours. Then, solvent was distilled from the solution under reduced pressure. The obtained residue was washed three times with tetrahydrofuran, and dried at 100degreesC for 24 hours, to obtain white product (7.3). The white product was tetrakis(pentafluorobenzene thiolate)lithium borate according to infrared spectrum. The obtained product was insoluble in water or common organic solvent. Swelling of the product was not observed even when it was left in water for long period of time, which confirmed that the product was excellent in water-proof property. The decomposition of the product was not observed during thermogravimetric analysis performed at room temperature-200degreesC, which confirmed that the product had high heat stability. The pellet obtained by hot-pressing the obtained product at 190degreesC, had ion electroconductivity of 10-9 Scm-1. The obtained lithium salt (0.1) was dispersed in polyethylene oxide (0.1), to obtain a mixture. The obtained mixture was made into lithium ion conductive liner sheet by hot-pressing at 90degreesC. The obtained liner sheet had excellent electroconductivity at 30-80degreesC.