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Artificial graphite (AG), in contrast to natural graphite, has received much attention due to its superior rate capabilities and stability under high current density. Although the rate capabilities can be enhanced by employing artificial graphite, there is room for improvement in the cycle retention characteristics of artificial graphite. In particular, further optimization on the binder type on anodes is necessary, as commercially used polyvinylidene fluoride (PVdF) has limitations in long-term cycling stability. Furthermore, PVdF is dissolved in N-Methyl-2-pyrrolidone (NMP), which is not environmentally- and eco-friendly. In this work, we have introduced a water-soluble binder based on deacetylated kondagogu gum (KG) for AG anodes, which are derived from the gum tree. Upon deacetylation, kondagogu gum can be dissolved in water, which can be directly used together with active materials and conductive agents in a slurry. Replacing a PVdF binder with a KG binder results in an enhanced cycle retention and comparable rate capabilities, without the changes in the overall redox reactions with Li+. Postmortem analysis reveals that the improved electrochemical performance of the AG anode contributed to the excellent structural integrity of the KG binder compared with the PVdF binder.

Abstract To realize the development of high‐performance electrodes materials, real‐time observation tool that can visualize dynamical changes of electrode materials upon lithiation and sodiation is highly critical. Recently, in situ transmission electron microscopy (TEM) has gained much attraction as it provides rich information on both phase and morphological transitions of electrode materials upon lithiation and sodiation in an atomic scale. Nevertheless, two significant limitations are present for current in situ TEM study: i) most of the in situ TEM experiments use a specially designed TEM holder, which is costly and suitable for use in only selective types of TEM; and ii) recently developed in situ TEM techniques with no applied bias have inherent limitations in the size of the sample (difficult for a size above 50 nm). Overcoming these two aforementioned issues, bias‐free graphene solid cells (GSCs) are now introduced, which can conduct real‐time observation of electrode materials in any size dimensions and morphologies without using bias. In this work, dynamical changes of hollow SnO2 nanotubes (NTs) are visualized upon lithiation and sodiation in real time using GSCs, where rich information is obtained on the morphology‐dependent, ion‐dependent characteristics of dynamical changes.

Electrochemical reactions can generate stresses that detrimentally affect battery electrodes. Here, the authors directly image the lithiation of core-shell tin-based nanoparticles and show that lithium can be redistributed by applying stress and change the nanoparticle composition.

Copper sulfide allows for high-performance sodium ion storage, yet its sodiation mechanism is poorly understood. Here, the authors examine the atomic structures of sodiated phases via in situ transmission electron microscopy, showing a non-equilibrium reaction pathway.

Abstract Finding suitable electrode materials is one of the challenges for the commercialization of a sodium ion battery due to its pulverization accompanied by high volume expansion upon sodiation. Here, copper sulfide is suggested as a superior electrode material with high capacity, high rate, and long‐term cyclability owing to its unique conversion reaction mechanism that is pulverization‐tolerant and thus induces the capacity recovery. Such a desirable consequence comes from the combined effect among formation of stable grain boundaries, semi‐coherent boundaries, and solid‐electrolyte interphase layers. The characteristics enable high cyclic stability of a copper sulfide electrode without any need of size and morphological optimization. This work provides a key finding on high‐performance conversion reaction based electrode materials for sodium ion batteries.