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.
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. There has been a fair amount of work exploring the development and performance of stretchable electrodes, but very little for stretchable electrolytes. Solid polymer electrolytes are ideal candidates for creating fully stretchable lithium ion batteries because of 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. We have investigated 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 growth with respect to the tensile strain. This increasing trend in conductivity infers that the structural changes induced in the polymer electrolyte results in altered and improved ion conduction. 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. We hypothesize that the stretching and aligning of the amorphous polymer chains decreases the degree of tortuosity in the polymer, allowing for faster, and less obstructed ion transport. Semi-crystalline PEO consists of a crystalline phase and an amorphous phase. The amorphous phase is generally present along the edges of the crystallites where the polymer chains are disordered, twisted and entangled and tie one crystallite to another. The semi-crystalline conformation of PEO can be seen using polarization light microscopy, which confirms the growth and extension of the amorphous regions as the chains stretch and disentangle due to tensile strain. In conclusion, the present work confirms the feasibility of using solid polymer PEO as a stretchable electrolyte for next generation stretchable batteries.
Objective Lithium ion batteries (LIBs) have attracted much attention over the past 15 years as the energy source of cell phones, laptops, power tools, medical equipment, and entertainment devices. Low self-discharge rate, high energy density, temperature tolerance, and long life-time are the advantages that LIBs offer over any other sort of batteries1. In addition, a considerable market growth is predicted for LIBs in future as a part of automobile industry where they power Hybrid Electrical Vehicles (HEVs), and Electrical Vehicles (EVs). To achieve the practical values that make LIBs applicable for EVs and HEVs, a lot of developments with the purpose of increasing capacity, safety, and life-time of the batteries have been investigated. Synthesis of new materials for the negative electrode of LIBs is a major component of this development. New anode materials have been synthesized with improved capacity, charge/discharge rates, and safety. However, their volume expansion during lithium intercalation/deintercalation is the major problem of these electrodes, which prevents their commercialization. Till date, the commercial anode material for LIBs has been graphite. However, graphite, as anode material for high energy/power density LIBs, suffers from low theoretical capacity and multitude of aging mechanisms. One of the major aging mechanisms is growth of solid electrolyte interface (SEI) layer on graphite, which results in loss of recyclable lithium ions and electrode material. This phenomenon unfavorably affects the life-time of the battery and makes the graphite electrode very vulnerable2,3. Moreover, capacity loss and degradation of graphite, in used LIBs, disqualifies graphite anodes for recycling as a high quality material during LIBs recycling processes. The overall research objective of this research is improving graphite electrode’s mechanical and electrochemical properties for LIBs that can deliver higher capacities while decreasing graphite degradation and irreversible capacity. This goal will be accomplished by: Graphite surface modification by placing a thin layer of carbon coated Fe3O4 nanoparticles (NPs) on graphite’s surface as an artificial solid electrolyte interface layer. This method is expected to improve LIBs applications in HEVs and EVs and provide potential graphite recycling opportunities. Methodology Fe3O4 NPs will be synthesized4 and assembled on graphite by a solution-phase self-assembly method5. This method involves mixing two immiscible solutions of Fe3O4 NPs and graphite under sonication. The graphite/Fe3O4 NPs is expected to deliver higher capacity, decrease irreversible capacity during formation stage, and reduce graphite degradation during operating cycles. The electrochemical properties of the proposed electrode will be tested in a coin cell. These tests will employ cyclic voltammetry as well as constant current galvanic cycling. This will allow the capacity of the electrode material to be found experimentally as a function of charge/discharge rate, as well as the capacity windows that the electrochemical reactions take place. In order to characterize the electrode material, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Atomic Frequency Microscopy (AFM) will be utilized. References Yoshino, A., The Birth of Lithium-Ion Battery. Angewandte Chemie-international Edition, 2012, 51(24), 5798. Agubra, V.; Fergus, J. Lithium Ion Battery Anode Aging Mechanisms. Materials, 2013, 6, 1310. Wang, H. Y.; Wang, F. M. Electrochemical Investigation of an Artificial Solid Electrolyte Interface for Improving the cycl-ability of Lithium Ion Batteries Using an Atomic Layer Deposition. J. Power source, 2013, 233,1. Sun, S.; Zeng, H.; Robinson, D. B. Robinson; Raoux, S.; Rice, P. M.; Wang, S. X., Li, G. Monodisperse Magnetic Nanoparticles for Theranostic Applications. J. Am. Chem. Soc. 2004, 126, 273. Guo, S.; Sun, S. FePt Nanoparticles Assembled on Graphene as Enhanced Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2012, 134, 2492.
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