A LiMn 2 O 4 (LMO) containing three-dimensional composite cathode was prepared by impregnation of carbon fiber paper with the oxide precursor sol. The sol consisted of the corresponding metal acetates, instead of nitrates in order to prevent the evolution of nitrous gases during the calcination. Poly(vinylpyrrolidone) served as chelating agent, which allows for a homogeneous distribution of the metal ions in the sol. Carbon fiber paper was soaked with the precursor sol and dried repeatedly up to the desired filling grade. After gelation of the precursor sol, the gel was converted to LMO at 450 • C. At this temperature transformation of the amorphous gel into crystalline LMO was completed and in the same time it was possible to retain the carbon backbone without significant material damage. The carbon fiber matrix serves as the three-dimensional support for the LMO particles and current collector in the oxide/carbon composite. Microstructural characterization of the LMO/carbon composites revealed that LMO crystals were deposited directly onto the carbon fibers as well as in the voids between the fibers which results in a homogeneous distribution of active material throughout the cathode's bulk. Electrochemical properties of the composite cathodes were investigated as a function of the number of sol impregnation steps. It was noted that the specific capacity of the cathode increases with the number of fillings. Moreover, the irreversible capacity regarding the first charge/discharge cycles was greatly reduced. As proof-of-concept a lithium-ion battery cell containing dry solid polymer electrolyte was assembled and its electrochemical performance was evaluated for future solid-state battery application. Lithium-ion batteries (LIBs) are one of the most attractive energy storage systems for future applications due to their high energy densities. However, safety and toxicity concerns still remain in commercial LIBs equipped with organic liquid electrolyte.1 By replacing the liquid electrolyte with a lithium-ion conducting polymer-based or ceramic electrolyte, these issues may be resolved and will result in inherent cell safety and increased energy density.2 These so called solid-state lithium-ion batteries (SSBs) have been extensively studied with regards to the ionic conductivity of the electrolytes and the interfacial issues between the electrode active materials and electrolyte. [3][4][5][6] In order to realize SSBs with increased energy density metallic lithium as anode material has to be applied in the cell necessarily. However, to fully leverage this advantage, the practical capacity on the cathode side needs to be adjusted accordingly. Unfortunately, lithium metal oxide materials used commonly as cathode active material, such as LiFePO 4 or LiMn 2 O 4 , are poor electric and ionic conductors, 7 which limit the useable thickness of the cathode. In liquid electrolyte based LIBs addition of electrical conductive additives to the active material and formulation of highly porous electrode layers (soaked afterwards w...