Structural analysis of non-stoichiometric lithium cuprates, Li2+2xCu1-2xO2-x. Effects of lithium content and thermal treatments

Lithium cuprate (Li2CuO2) is being used for a wide range of applications due to its high lithium diffusion through the layer structure. Moreover, Li2+2xCu1-xO2-x non-stoichiometric material shows enhanced physicochemical properties. Therefore, lithium location understanding is highly important for lithium cuprate applications. This paper reports the structural coherence analysis, local and long atomic arrangement of Li2+2xCu1-xO2-x using X-ray diffraction (XRD), pair distribution function (PDF) and solid-state nuclear magnetic resonance (NMR) techniques. Li2CuO2, containing different excess quantities of lithium (from 0 to 60 at%), were synthesized by solid-state reaction. The synthesized ceramics presented nonstoichiometric structures, with Li2CuO2 type-structure. Two structural models were proposed to explain the high enhancement physicochemical properties of these ceramics; (i) the extra lithium atoms substitute copper sites, and (ii) lithium species occupy interstitial sites in the crystalline structure. Additionally, further thermal treatments rearrange the non-stoichiometric crystalline structures into the stable Li2CuO2 phase.