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The structural transformations occurring during the intercalation of lithium into disordered graphite in a working battery were studied in detail by operando X‐ray powder diffraction (XRPD). By using a capillary‐based micro‐battery cell, it was possible to study the stacking disorder in the initial graphite as well as in lithiated graphites. The micro‐battery cell was assembled in its charged state with graphite as positive electrode and metallic lithium as counter electrode. The battery was discharged until a stage II compound (LiC12) was formed. The operando XRPD data reveal that the graphitic electrode material retains a disordered nature during the intercalation process. A DIFFaX+ refinement based on the initial operando XRPD pattern shows that the initial graphite generally has an intergrown structure with domains of graphite 2H and graphite 3R. However, the average stacking sequence of the initial graphite also contains a significant concentration of AA‐type stacking of the graphene sheets. DIFFaX+ was further used to refine structure models of a stage III type compound and the final stage II compound. The refinement of the stage II compound showed that it is dominated by AαAAαA‐type stacking, but that it also contains a significant concentration of AαABβB‐type slabs in the average stacking sequence. [ABSTRACT FROM AUTHOR]

A novel capillary-based micro-battery cell for in situ X-ray powder diffraction (XRPD) has been developed and used to study the initial intercalation and deintercalation of lithium into graphite in a working battery. The electrochemical cell works in transmission mode and makes it possible to obtain diffraction from a single electrode at a time, which facilitates detailed structural and microstructural studies of the electrode materials. The micro-battery cell is potentially also applicable for in situ X-ray absorption spectroscopy and small-angle X-ray scattering experiments. The in situ XRPD study of the initial intercalation and deintercalation process revealed marked changes in the diffraction pattern of the graphitic electrode material. After the formation of the solid electrolyte interphase layer, the d spacing of the diffraction peak corresponding to the 002 diffraction peak of graphite 2H changes nearly linearly in two regions with slightly different slopes, while the apparent half-width of the diffraction peak displays a few minima and maxima during charging/discharging. DIFFaX+ refinements based on the initial XRPD pattern and the one after the initial discharging-charging cycle show that the structure of the graphite changes from an intergrown structure of graphite 2H and graphite 3R to a nearly ideal graphite 2H structure. DIFFaX+ was also used to refine a model of the stacking disorder in an apparent stage III compound with Aα AB- and Aα AC-type slabs. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) and reduced graphene oxide (rGO) are important materials in a wide range of fields. The modified Hummers methods, for synthesizing GO, and subsequent thermal reduction to rGO, are often employed for production of rGO. However, the mechanism behinds these syntheses methods are still unclear. We present an in situ X-ray diffraction study of the synthesis of GO and thermal reduction of GO. The X-ray diffraction revealed that the Hummers method includes an intercalation state and finally formation of additional crystalline material. The formation of GO is observed during both the intercalation and the crystallization stage. During thermal reduction of GO three stages were observed: GO, a disordered stage, and the rGO stage. The appearance of these stages depends on the heating ramp. The aim of this study is to provide deeper insight into the chemical and physical processes during the syntheses. [ABSTRACT FROM AUTHOR]

To develop more efficient and safer batteries, a deeper understanding of lithium ion intercalation and de-intercalation dynamics upon operation in lithium-ion batteries is of great importance. We have performed operando high-resolution powder X-ray diffraction (PXRD) studies of the intercalation and de-intercalation process in a graphite electrode material using custom-made capillary-based lithium-ion battery cells. Using high-resolution PXRD, it was possible to resolve the diffraction peaks from a number of lithiated graphite phases occurring during intercalation/de-intercalation of lithium and obtain information about the transformation processes, both related to the staging process and the in-plane transformation. In the staging related to the intercalation of lithium, two-phase and solid-solution behavior is identified. Similar phase behavior is observed when examining the in-plane parameters. The mechanism of intercalation is proposed to involve charge transfer between the lithium ion and the π orbitals of the graphene layer. Broadening of the hk0 peaks may be related to non-uniform reduction of the graphene layers depending on the staging number and the graphene layer neighboring environment. Image 1 [ABSTRACT FROM AUTHOR]