Abstract
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.
Highlights
Over the past decades, the conventional rigid batteries and supercapacitors have progressively evolved into smaller, thinner, and flexible devices[1,2,3]
The conductivity in the perpendicular direction, has been observed to decrease and was attributed to the stiffening of the polymer chains, suppression in ion hopping between chains, and the alignment of polyethylene oxide (PEO) helices oriented in the force direction, leaving only a few helices oriented in the
If the behavior of a specimen is predominantly elastic in nature, the stresses are generally governed by forces carried within the amorphous and crystalline phase structures as well as viscous forces[28]
Summary
The conventional rigid batteries and supercapacitors have progressively evolved into smaller, thinner, and flexible devices[1,2,3]. We focus on stretchable solid polymer electrolytes (SPEs) for potential use in a fully stretchable battery. The polymer electrolytes that do exhibit higher ion conductivities typically lack sufficient mechanical stability – they are either in the form of a gel electrolyte (composed of solid and liquid phases) or consist of lower molecular weight polymers. Most common methods for achieving improved ion conductivity without compromising the mechanical integrity of the SPEs consist of introducing nanofillers[9,10,11,12] into the polymer matrix or, alternatively, using polymer blends[8,9,13,14,15]. The lithium ions are transported by the repeated thermally driven motion of the polymer chain segments, which creates new coordination sites that the ions use to migrate through the electrolyte[14]. The measurements methods for in-plane and through-plane ion conductivities have been discussed previously[26,27]
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