Designing, synthesizing, and monitoring battery materials using advanced operando techniques
Since the commercialization of lithium-ion (Li-ion) batteries by Sony in 1991 , researchers have been extensively working on increasing the specific energy of both negative and positive electrode materials by replacing, respectively, graphite and LiCoO2 used therein. Although the specific energy of Li-ion batteries can be slightly increased, this nearly 30-year-old intercalation-chemistry-based battery technology is approaching its limitations. One of the opportunities for Li-ion batteries to keep up with the rapid pace of device development and outperform current Li-ion batteries is to replace the traditional graphite negative electrode. In response to this, the research is currently focused on conversion or alloying materials (Sn, Sb, P, Si). Although these materials have significantly higher specific charges than that of graphite, during cycling they do experience huge volume changes of at least 200%, which results in mechanical strain . In parallel, other battery chemistries based on Na-ion chemistry or on solid electrolytes have received considerable attention. During electrochemical cycling, these battery systems exhibit new and/or less explored reaction mechanisms at the bulk and the interface/surface levels, the investigation and understanding of which require new characterization tools . There are two different approaches to understand the reaction mechanism of electroactive materials during cycling, namely using either ex situ or in situ/operando modes. For the latter approach, the development of reliable electrochemical cells is of a prime importance. This is never an easy task though, since the design of such cells has to be adequate to the technique of a choice and its individual requirements. Once a proper design is, however, found, the surface, the bulk, the interphases, and finally the combination of these can be studied and the reaction mechanisms can be better understood and/or elucidated, thus further improving the battery technology. In the first part of the talk, it will be described how to increase the specific charge of the electrodes by modifying the synthesis strategy as well as “playing” with the surface and interfaces. The second part will focus on the analysis of the electrochemical reactions occurring during cycling of selected materials by combination of different operando/in situ studies like X-ray diffraction, neutron diffraction, neutron imaging and X-ray tomographic microscopy etc.
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