Short and Intermediate Range Ordering in Fast Cation Glasses for Battery Applications

Abstract

Lithium batteries provide the highest energy density which makes them ideal candidates for future generations of portable electronics (laptops, cellular, tablets, etc.) and hybrid electric vehicles for the time being. However, the increasing demand for lithium batteries will be limited by the fact that lithium is not an abundant material and its cost is expected to increase considerably in the coming years. In contrast, sodium resources are unlimited (fourth most abundant element in Earth’s crust) and from economic point of view, sodium batteries appear as good alternative to lithium devices, particularly for large-scale stationary applications. The ionic conductivity of chalcogenide and chalcohalide glasses is 2 to 3 orders of magnitude higher than that of oxide glasses with the same mobile ion content. This makes chalcogenide systems suitable for applications in power rechargeable systems. Our studies are focused on the development of new Na+ion-conducting chalcohalide glasses combining sodium halides and sulfide-based glass network. Cation local environment and intermediate-range ordering in glasses are critically important to achieve fast ionic conduction. Usual structural hypothesis related to superionic glasses containing metal halides MY = LiI, NaBr, AgI, etc., implies the absence of chemical interactions between the host glass and metal halide. An expansion of the host network caused by large anions (I, Br) and related increase of the available free volume for fast cations, forming preferential conduction pathways, was considered to be the key parameter for glassy superionics. Nevertheless, recent studies of AgY and CuY crystalline coordination polymers show chemical interaction between metal halide and chalcogenide backbone giving rise to mixed M-centered polyhedra. The polyhedral connectivity was also found to be different, starting from isolated units and dimers and finishing by chains, 2D layers and tubes. Some characteristic types of MY-subnetwork are given in Fig. 1(a,b). Using pulsed neutron and high-energy x-ray diffraction combined with Reverse Monte Carlo modelling, we examine cation local and intermediate range ordering in two glassy systems containing either silver iodide or sodium halides. Sodium chalcogenide glasses exhibit high ionic conductivity and seem to be promising for battery applications. Figure 1