Electrochemical behavior of lithium intercalated in a molybdenum disulfide-crown ether nanocomposite

Abstract

A new nanocomposite, obtained from the intercalation of the cyclic ether 12-Crown-4 into MoS 2, Li 0.32MoS 2(12-Crown-4) 0.19, is described. The laminar product has an interlaminar distance of 14.4 Å. The electrical conductivity of the nanocomposite varies from 2.5 × 10 −2 to 4.3 × 10 −2 S cm −1 in the range 25–77 °C, being about four times higher than the analogous poly(ethylene oxide) (PEO) derivative at room temperature. The electrochemical step-wise galvanostatic intercalation or de-intercalation of lithium, leading to Li x MoS 2(12-Crown-4) 0.19 with x in the range 0.07–1.0, indicates a Li/Li + pair average potential of 2.8 V. The electrochemical lithium diffusion coefficients in the crown ether intercalates, determined by galvanostatic pulse relaxation between 15 and 37 °C at different lithium intercalation degrees, are higher than those of the PEO derivatives under similar conditions, being however the diffusion mechanism rather more complex. The variation of both, the lithium diffusion activation enthalpy and the quasi-equilibrium potentials, with the lithium content shows there are two different limit behaviors, at low and high lithium intercalation degree, respectively. These features are discussed by considering the high stability of the Li-crown ether complex and the different chemical environments found by lithium along the intercalation process.