PYROCARBON COATING ON CARBONAIZED PAPER FOR ANODE OF LITHIUM-ION SECONDARY BATTERY AND ITS ELECTROCHEMICAL PROPERTIES IN PROPYLENE CARBONATE BASE ELECTROLYTE

摘要

Using PCVI technique, pyrocarbon film was coated at 950°C from C_3H_8 (30%) - H_2 gas system on the hard carbon fibers prepared by the carbonization of the filter paper. Carbon fibers were coated with the dense pyrocarbon films having the laminar texture oriented parallel to the surface of the carbonized fiber. It was revealed from XRD and Raman spectroscopy that the crystallinity of pyrocarbon is higher than that of the carbonized fiber. BET surface area was decreased from 223 m~2 g~(-1) of original substrate to 1.9 m~2 g_(-1) of the pyrocarbon-infiltrated sample. Electrochemical properties were measured in EC and PC base electrolytes. Reversible capacity of the coating sample was 450-500 mA h g~(-1) in each electrolyte, which was nearly close to that of the original carbonized paper. High irreversible capacity was observed in the original carbonized paper, reflecting the disordered structure and high surface area. Irreversible capacity was reduced in EC-based electrolyte by coating with 18 mass% pyrocarbon, which would be attributed to the high crystallinity, laminar structure and low surface area of pyrocarbon. Irreversible capacity was also decreased in PC-based electrolyte. The crystallinity of pyrocarbon was not so high as graphite, on which PC-based electrolyte was decomposed.