Enhanced safety of flexible batteries is an imperative objective due to the intimate interaction of such devices with human organs such as flexible batteries that are integrated with touch-screens or embedded in clothing or space suits. In this study, the fabrication and testing of a high performance thin-film Li-ion battery (LIB) is reported that is both flexible and relatively safer compared to the conventional electrolyte based batteries. The concept is facilitated by the use of solid polymer nanocomposite electrolyte, specifically, composed of polyethylene oxide (PEO) matrix and 1 wt% graphene oxide (GO) nanosheets. The flexible LIB exhibits a high maximum operating voltage of 4.9 V, high capacity of 0.13 mA h cm(-2) and an energy density of 4.8 mW h cm(-3). The battery is encapsulated using a simple lamination method that is economical and scalable. The laminated battery shows robust mechanical flexibility over 6000 bending cycles and excellent electrochemical performance in both flat and bent configurations. Finite element analysis (FEA) of the LIB provides critical insights into the evolution of mechanical stresses during lamination and bending.

There is a strong need in developing stretchable batteries that can accommodate stretchable or irregularly shaped applications including medical implants, wearable devices and stretchable electronics. Stretchable solid polymer electrolytes are ideal candidates for creating fully stretchable lithium ion batteries mainly due to their mechanical and electrochemical stability, thin-film manufacturability and enhanced safety. However, the characteristics of ion conductivity of polymer electrolytes during tensile deformation are not well understood. Here, we investigate the effects of tensile strain on the ion conductivity of thin-film polyethylene oxide (PEO) through an in situ study. The results of this investigation demonstrate that both in-plane and through-plane ion conductivities of PEO undergo steady and linear growths with respect to the tensile strain. The coefficients of strain-dependent ion conductivity enhancement (CSDICE) for in-plane and through-plane conduction were found to be 28.5 and 27.2, respectively. Tensile stress-strain curves and polarization light microscopy (PLM) of the polymer electrolyte film reveal critical insights on the microstructural transformation of stretched PEO and the potential consequences on ionic conductivity.

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Flexible and stretchable energy storage devices, including batteries, supercapacitors, and ionic piezoelectrics, have garnered substantial research interest in recent years to address a wide range of applications such as smart textiles and medical implants. These devices are intended to undergo mechanical deformation, and the impact of deformation on electrochemical performance is not well understood. One important area of focus is studying how mechanical deformation influences ion conduction in polymer electrolytes. In this work, a dual theoretical and experimental approach is taken to further evaluate this phenomenon. A stretchable solid polymer electrolyte film subjected to tensile deformation (approximately 48% strain), through which ion diffusion occurs, is analyzed using a continuum approach treating ion diffusion and mechanical deformation as coupled. Thermodynamic laws are applied to obtain governing multiphysics equations accounting for large deformation mechanics and material nonlinearity. The theoretical solution obtained demonstrates how through-plane ionic conductivity changes when the polymer is subjected to stretching. Evolutionary materials deformation of the polymer electrolyte is considered to elucidate the underlying driving physical mechanisms of ion conduction. An experiment was also conducted to measure change in through-plane ionic conductivity with applied uniaxial strain in a sample of polyethylene oxide (PEO), a material commonly used as the electrolyte in solid polymer electrolyte lithium ion batteries. The experimental results show a greater than 1600% ionic conductivity enhancement for approximately 48% strain. The theoretical and experimental results are in good agreement and show that ion conduction is enhanced with increasing strain following an exponential function for a PEO electrolyte.

This article is an introduction to lithium-ion (Li-ion) battery types, types of failures, and the forensic methods and techniques used to investigate the origin and cause to identify failure mechanisms. This article discusses common types of Li-ion battery failure with a greater focus on the thermal runaway, which is a particularly dangerous and hazardous failure mode. Forensic methods and techniques that can be used to characterize battery failures will also be discussed. This is the first article in a six-part series. The first article describes ways in which Li-ion batteries can fail, followed by a discussion of challenges assessing the reliability of such a rapidly evolving technology in article two. The third article discusses potential mitigation strategies for BESS facilities, and the fourth article discusses the consequences of catastrophic failure in a BESS. Article five provides a review of available analytical approaches to evaluate existing structures and design new structures for protection from Li-ion battery hazards. The final article is an overview of Li-ion BESS failures and risk management considerations.