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.

The mass point leak rate technique is often the methodology of choice for quantifying leak rates as it uses simple elementary measurements, applies to gas systems of low mass, proves effective for low leak rates, and does not rely on test-gas conversions. In this methodology, a number of instantaneous mass measurements are calculated through samples of volume, pressure, gas composition, and temperature measurements over time. A regression analysis of the corresponding mass-time sample set yields the leak rate of the system. A detailed uncertainty analysis is paramount for a complete, experimental characterization of the leak rate and previously was not fully implemented in the mass point leak rate method. Recent advancements in regression uncertainty analysis by propagation of errors afford the ability to quantify the uncertainty with estimates of covariance in the regression results. The mass point leak rate technique with the associated detailed measurement uncertainty analysis offers the ability to quantify both the leak rate and the uncertainty associated with the leak rate value. Detailed herein is the development of the methodology and a detailed uncertainty analysis that includes both precision (repeatability) and bias (systematic) error. Alternative leak rate methods are also discussed for comparison purposes. An example in the methodology is presented.

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