(US5965299-A)      A composite electrolyte comprises; (a) surface-modified fumed silica filler, surface-crosslinked with polymerisable groups to give a three-dimensional structure; (b) a dissociable lithium salt; and a bulk medium containing (a) and (b) above.    Also claimed are: (i) an electrochemical cell comprising anode, cathode and the electrolyte claimed above interposed between them; (ii) a battery comprising anode, cathode with the electrolyte above between them; and (iii) a method of producing the electrolyte above comprising reacting fumed silica with a surface reactive monomer to modify the surface and contacting it with a bulk medium comprising the lithium salt, an initiator and a monomer which does not react with the silica surface but can react with the polymerisable group; the mixture then being formed into a defined geometry and polymerised so that the polymerisable groups on the silica surface become bonded and a three-dimensional composite is formed.    USE -   As electrolytes for electrochemical cells and batteries    ADVANTAGE -   The electrolyte has good mechanical properties, high conductivity at room temperature and is easy to process.    (EP1038330-A1)      A composite electrolyte comprises; (a) surface-modified fumed silica filler, surface-crosslinked with polymerisable groups to give a three-dimensional structure; (b) a dissociable lithium salt; and a bulk medium containing (a) and (b) above.    Also claimed are: (i) an electrochemical cell comprising anode, cathode and the electrolyte claimed above interposed between them; (ii) a battery comprising anode, cathode with the electrolyte above between them; and (iii) a method of producing the electrolyte above comprising reacting fumed silica with a surface reactive monomer to modify the surface and contacting it with a bulk medium comprising the lithium salt, an initiator and a monomer which does not react with the silica surface but can react with the polymerisable group; the mixture then being formed into a defined geometry and polymerised so that the polymerisable groups on the silica surface become bonded and a three-dimensional composite is formed.    USE -   As electrolytes for electrochemical cells and batteries    ADVANTAGE -   The electrolyte has good mechanical properties, high conductivity at room temperature and is easy to process.