Dip-Coating of Carbon Fibers for the Development of Lithium Iron Phosphate Electrodes for Structural Lithium-Ion Batteries

This study describes a dip-coating method for applying an active material to commercially available intermediate modulus carbon fibers (CFs). A suite of tools were developed to assist with the handling and coating of CF tows to create disc electrodes. CF electrodes were fitted into 2025-type coin cells, for electrochemical analysis, first to determine their performance as anodes. Specimens of CFs were dip-coated with a slurry consisting of lithium iron phosphate, carbon black, and polyvinylidene fluoride, then dried, and fitted into half-cells to analyze the cathode performance. A cyclic voltammetry sweep was performed on each half-cell to determine suitable cycling potential limits, followed by galvanostatic cycling for a minimum of 30 cycles. Measured capacities for anode and cathode half-cells yielded 92 and 52.3 A h kg-1, respectively. A full-cell with CFs in both electrodes was assembled and tested, revealing a capacity of 24.7 A h kg-1 after 30 cycles. Finally, both the anode and cathode were examined with a scanning electron microscope to establish a benchmark (anode) to compare surface topologies and to analyze the quality of the active material applied via dip-coating (cathode).