Lithium Insertion in Disordered Carbons Prepared from Organic Polymers

Abstract

Disordered carbon samples were prepared from four organic polymers: poly[(Z)-1-methoxy-4-phenyl-1-buten-3-yne] [poly(MPBEY)], poly(1,4-diphenyl-1-buten-3-yne) [poly(DPBEY)], poly[5-(2-pyridyl)-2,4-pentadiyn-1-ol] [poly(PyPDO)], and poly(2,4-hexadiyn-1,6-diol) (PHDO). Electrochemical Lithium insertion into these disordered carbons was studied with discharge/charge tests, cyclic voltammetry, and Li-7 nuclear magnetic resonance (NMR) spectroscopy. Ln the potential range of 0.0 to 2.5 V vs. Li/Li+, all carbons showed discharge/charge curves with a hysteresis effect unlike typical curves for standard lithium insertion/removal processes in pyrolyzed carbons. This hysteresis may be caused by the lithium-oxygen bonding of the organolithium complexes. Li-7 NMR spectra showed two kinds of lithium insertion sites in all carbons: a reversible site from which lithium could be removed in the subsequent charge process and an irreversible site where lithium remains intact. The NMR results suggest that the reversible site lithium has ionic nature in all of the fully Li-inserted carbons.