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Flexible Li‐ion batteries (LIBs) have a strong oncoming consumer market demand for use in wearable electronics, flexible electronics, and implantable medical devices. This market demand necessitates research on flexible LIBs to fulfill the energy requirements of these devices. One of the main areas of research of flexible LIBs is the active and inactive materials used in manufacturing these batteries. Active materials are those used in the battery electrodes to store lithium in their structure. The remaining materials in flexible LIBs, which do not directly contribute to energy storage, are inactive materials. Inactive materials and components—including electrode conductive materials, binders, separator, current collectors, electrolyte, and casing/packaging—make up almost 60% of the total weight of a LIB. Thus, they are important in the determination of energy and power density of flexible LIBs. This study reviews the inactive materials and components of flexible LIBs from two aspects. First, inactive materials and components used in flexible LIBs and their properties are compared. Then, the compatibility and stability of inactive materials and components are discussed. Overall, this article gives an extensive insight to researchers on inactive materials and components employed so far for flexible LIBs.

In this study, synchrotron X-ray computed tomography has been utilized using two different imaging modes, absorption and Zernike phase contrast, to reconstruct the real three-dimensional (3D) morphology of nanostructured Li 4 Ti 5 O 12 (LTO) electrodes. The morphology of the high atomic number active material has been obtained using the absorption contrast mode, whereas the percolated solid network composed of active material and carbon-doped polymer binder domain (CBD) has been obtained using the Zernike phase contrast mode. The 3D absorption contrast image revealed that some LTO nano-particles tend to agglomerate and form secondary micro-sized particles with varying degrees of sphericity. The tortuosity of electrode's pore and solid phases were found to have directional dependence, different from Bruggeman's tortuosity commonly used in macro-homogeneous models. The electrode's heterogeneous structure was investigated by developing a numerical model to simulate galvanostatic discharge process using the Zernike phase contrast mode. The inclusion of CBD in the Zernike phase contrast results in an integrated percolated network of active material and CBD that is highly suited for continuum modeling. The simulation results highlight the importance of using the real 3D geometry since the spatial distribution of physical and electrochemical properties have a strong non-uniformity due to microstructural heterogeneities.

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