Synthesis and Characterization of New Intercalated Lithium Cathodes

Abstract

Layered MPX_n (n = 3 and 4) have a structure closely related to the CdI₂ and CdCl₂ types. In their Van der Waal’s gap, they present octahedral sites. These sites are larger in the sulfide derivatives than in the corresponding disulfides of transition elements. In the octahedral interstices, lithium intercalates (M being a transition metal) without parameter expansion. Such property can be used in a battery MPX_n /electrolyte/Li, in which topochemical intercalation takes place electro-chemically. The synthesis and physical properties of the two dimensionnal phases have been completed, along with chemical and electrochemical lithium intercalation. A study on NiPS₃ showed this material to be stoechiometric. Only the MPX- group exhibited promising behaviour, and particularly NiPS₃, FePSe₃ and FePS₃. Open potential circuit and magnetic measurements, NMR of ⁷Li and ³¹P indicate that, in the case of Li_x NiPS₃ (O < x < 1.5), the intercalation takes place through two phases (Li_0.5 Nips₃ and Li_1.5Nips₃). High current density discharge curves carried out on the three above compounds have revealed some solvent interaction during intercalation. Such interaction improves the reversibility of the generator, at least in the case of NiPS₃.