A lithium-ion-conducting composite material, comprising at least one polymer and lithium-ion-conducting particles, characterized in that the interfacial resistance for lithium ion conductivity between the polymer and the particles is decreased due to a surface modification of the particles, and therefore the lithium ion conductivity is greater than for a comparable composite material in which the interfacial resistance between the polymer and the particles is not decreased, the interfacial resistance for lithium ion conductivity being measured by way of the method provided in the description, the surface modification being selected from the group consisting of silanization, functionalization with a short-chain liquid polyethylene glycol, coating with a lithium-conducting material and/or coating with a ceramic material, and/or a combination thereof, the particles being made of a material having a garnet-like crystal phase with the empirical formula Li 7+x-y Mx" M 3-x III M 2-y IV M y V O 12, where M II represents a divalent cation, M III represents a trivalent cation, M IV represents a tetravalent cation, and M V represents a pentavalent cation, where 0 ≤ x < 3 and 0 ≤ y < 2 or of a material having a crystal phase isostructural to NaSICon, with the empirical formula Li 1+x-y M 5+ y M 3+ x M 4+ 2-x-y (PO 4) 3, where x and y are in the range from 0 to 1 and (1+x-y) > 1 applies, and M is a cation having a valence of +3, +4 or +5, the polymer being selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyesters, polypropylene oxide, ethylene oxide/propylene oxide copolymer, polyethylene oxide crosslinked with trifunctional urethane, poly(bis(methoxy-ethoxy-ethoxide)) -phosphazene (MEEP), triol-like polyethylene oxide crosslinked with difunctional urethane, poly((oligo)oxethylene) methacrylate-co-alkali metal methacrylate, polymethyl methacrylate (PMMA), polymethylacrylonitrile (PMAN), polysiloxanes, as well as the copolymers and derivatives thereof, polyvinylidene fluoride or polyvinylidene chloride as well as the copolymers and derivatives thereof, poly(chlorotrifluoroethylene), poly(ethylene-chlorotrifluoroethylene), poly(fluorinated ethylene-propylene), acrylate-based polymers, the condensed or crosslinked combinations thereof, and/or the physical mixtures thereof. the interfacial resistance for lithium ion conductivity between the polymer and the particles is decreased due to a surface modification of the particles, and therefore the lithium ion conductivity is greater than for a comparable composite material in which the interfacial resistance between the polymer and the particles is not decreased, the interfacial resistance for lithium ion conductivity being measured by way of the method provided in the description, the surface modification being selected from the group consisting of silanization, functionalization with a short-chain liquid polyethylene glycol, coating with a lithium-conducting material and/or coating with a ceramic material, and/or a combination thereof, the particles being made of a material having a garnet-like crystal phase with the empirical formula Li 7+x-y Mx" M 3-x III M 2-y IV M y V O 12, where M II represents a divalent cation, M III represents a trivalent cation, M IV represents a tetravalent cation, and M V represents a pentavalent cation, where 0 ≤ x < 3 and 0 ≤ y < 2 or of a material having a crystal phase isostructural to NaSICon, with the empirical formula Li 1+x-y M 5+ y M 3+ x M 4+ 2-x-y (PO 4) 3, where x and y are in the range from 0 to 1 and (1+x-y) > 1 applies, and M is a cation having a valence of +3, +4 or +5, the polymer being selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyesters, polypropylene oxide, ethylene oxide/propylene oxide copolymer, polyethylene oxide crosslinked with trifunctional urethane, poly(bis(methoxy-ethoxy-ethoxide)) -phosphazene (MEEP), triol-like polyethylene oxide crosslinked with difunctional urethane, poly((oligo)oxethylene) methacrylate-co-alkali metal methacrylate, polymethyl methacrylate (PMMA), polymethylacrylonitrile (PMAN), polysiloxanes, as well as the copolymers and derivatives thereof, polyvinylidene fluoride or polyvinylidene chloride as well as the copolymers and derivatives thereof, poly(chlorotrifluoroethylene), poly(ethylene-chlorotrifluoroethylene), poly(fluorinated ethylene-propylene), acrylate-based polymers, the condensed or crosslinked combinations thereof, and/or the physical mixtures thereof.