Liquid-Cell TEM Observations of Sn Lithiation Reactions: A Temperature Case Study

In recent years, the increasing use of portable electronics and the rise of eco-friendly electric vehicles put tremendous pressure on high-energy rechargeable lithium-ion batteries [1,2]. As a result, significant research has been focused on more advanced, high-capacity electrode materials such as Si, Sn, Ge and Li as anode and S and O2 as cathode materials [2-4]. These electrode materials are attractive due to their higher specific capacities than present commercial electrode materials such graphite (anode) and lithium metal oxides (cathode). However, issues like volume expansion, capacity fading and unwanted electrolyte reactions upon cycling prevent the commercialization of these electrode materials. Over the last decade, in order to address the degradation of high-capacity electrode materials, significant investigations have been carried out with in-situ/ operando S/TEM, X-ray diffraction, NMR, Raman and Mass spectroscopes [5]. In fact, to diagnose the effect of size and morphology of electrode materials at or near working electrochemical conditions, S/TEM can be used to visualize the lithium insertion and de-insertion of electrode materials at atomic resolution in some commercial volatile electrolytes such as organic carbonates. In addition, the electrode/electrolyte interface reactions can also be visualized while cycling. We are using a highly customized TEM liquid cell that successfully performs quantitative electrochemical control on ultramicroelectrodes for testing nanomaterials in volatile electrolytes during nanoscale imaging [6,7]. This design allows up to 10 electrodes incorporated into an even liquid gap of ~ 150-200 nm, where controlled assembly of nanomaterials onto the custom patterned electrodes allows for an ideally designed working cell inside the TEM.