Abstract

Operational safety and cycle stability are important attributes for all rechargeable batteries. To meet these stringent demands specifically for biomedical applications, an all-solid lithium-ion battery (ASLIB) consisting of a polyethylene oxide\ (PEO)-based polymer electrolyte with a lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, lithium titanate (LTO) anode and lithium iron phosphate (LFP) cathode is proposed. This work implements fabrication methods, composition optimizations and an assembly procedure, all tailored to the unique cell chemistry and ending in the all-solid LTO-PEO/LiTFSI-LFP cells. Subsequently, these ASLIBs are tested close to body temperature at 40 °C. This assures solid-state, but augments bulk electrolyte and interfacial resistance compared to frequent investigations of polymer electrolyte cells at even more elevated temperatures. In spite of these drawbacks, LTO-PEO/LiTFSI-LFP cells are successfully charged/discharged with a C-rate of C/20. In order to understand observed capacity fading, the cycling behavior of these cells is related to several electrochemical phenomena through impedance measurements and investigations of respective half- and symmetric cells. In the end, a unique electrode composition and assembly procedure is proposed to minimize interfacial resistance.

Highlights

  • 1.1 Motivation and ChallengesConventional lithium-ion batteries are favored for small and large-scale applications, from portable electronic devices to electric vehicles

  • The poly(ethylene oxide) (PEO)/lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) mixture is of a hygroscopic nature, contact with air during the fabrication can hinder drying of the electrolyte (Figure 3.4(b))

  • For an increasing weight fraction of BaTiO3, the results show a decreasing effect on the ionic conductivity for the solvent-free method and only a small conductivity enhancement for the solventbased procedure, which does not match the results stated in the literature

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Summary

Introduction

1.1 Motivation and ChallengesConventional lithium-ion batteries are favored for small and large-scale applications, from portable electronic devices (cell phones and laptops) to electric vehicles. The extent of optimization regarding it’s electrical and mechanical properties will influence how much ASLIBs can penetrate the battery market: The polymer electrolyte exhibits a lower ionic conductivity compared to conventional electrolytes, hindering high power applications. In order to circumvent this and end up with a comparable electrode structure, it is proposed to put small quantities of polymer electrolyte into anode and cathode during electrode processing. This would provide continuity at the electrode/electrolyte interface and diffusion pathways for lithium-ions into the electrode, facilitating accessibly to a larger portion of active material particles and increasing cell capacity

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