Structural and electrochemical study of Li+ insertion in the infrared reflectance modulating compound LixWO3·H2O

The structural and electrochemical behavior of o-LixWO3H2O has been studied for several electrochemical Li intercalation/deintercalation processes. Four intercalated phases called *a, *b, *g and *d, were distinguished by means of in situ X-ray diffraction (XRD) experiments. The modification in the distance between the tungsten layers represented by the cell lattice parameter b was found to reflect the structural changes induced by Li intercalation. Thus, we found that potential cycling over the *a phase (till x=0.35) does not lead to any major degradation of the structure whereas reducing further WO3H2O and reaching the *b, *g or *d phase introduces irreversible damages. Furthermore, the a intercalation domain divides into three subphases called *a0, *a1, and *a2. From the less intercalated phase to the most intercalated one, the structure exhibits increasing higher symmetry. The unintercalated orthorhombic cell (a( phase) first changes into a quasi-quadratic one where a #~ c#= b/2 (*a1 phase) and finally to a quasi-quadratic one where a #~ c #~ b/2 (*a2 phase). The knowledge of this intercalation behavior is essential to improve the performance of a recently built WO3DTH2O-based variable infrared reflectance plastic device.