Preparation and Characterization of a Polyethylene Oxide Based Composite Cathode

摘要

In the last years, there is increasing attention on all solid-state batteries due to safety reasons. In the state of the art of lithium ion batteries, organic solvents are used. The advantage of these solvents is the good penetration in the porous cathodes to ensure a good ion conductive contact with the active material. Mayor drawbacks are high flammability and leakage of the liquid electrolyte. Due to this reason, they should be replaced by non-volatile solid electrolytes. A change in the state of aggregation causes some adjustments relative to the cathode. Because solid electrolytes are not able to penetrate the cathode, the electrode has to consist of an additional lithium ion conductive part. Possible materials are ceramics like lithium lanthanum titanate (LLTO), glasses (LiPON, Li2S?P2S5) or polymers like polyethylene oxide (PEO) in combination with a lithium salt [1-2], for example lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The choice of the materials for the electrolyte was done by the means of conductivity, processability as well as availability. The aim is to produce stable cathodes containing the ion . conductor, the active electrode material, an electron conductor and additives, which perform in a sufficient way. Therefore, the well investigated electrolyte PEO/LiTFSI [3] was chosen as initial point for the first approaches. To optimize these systems, different compositions were prepared using the hot press method and characterized regarding the conductivity and electrochemical stability. Furthermore, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was added as an electronic conductor as well as lithium iron phosphate (LFP) as electrode active material. To produce a composite cathode, a slurry was prepared using these components and coated on an aluminum foil. The composite was characterized with SEM/EDX, impedance spectroscopy and other electrochemical methods.