Investigation of Parameters Governing the Charge Transfer Reaction in Organic Cathodes for Multivalent Batteries

Lužanin, Olivera (author), Bitenc, Jan (mentor), Cerkovnik, Janez (comentor)

The transition from fossil fuels to sustainable energy alternatives necessitates a significant advancement in our ability to store energy on a much larger scale. Safe and inexpensive batteries are crucial for this endeavor. The past decade has witnessed a sharp increase in interest in post-lithium-ion battery technology, including multivalent batteries. By combining energy-dense metal anodes, such as Mg and Ca, with environmentally friendly and structurally diverse organic cathodes, the full potential of multivalent technology might be achieved. Despite intensive research efforts, multivalent-metal-organic batteries still lag behind their monovalent counterparts in electrochemical performance, primarily in terms of cathode capacity utilization. This thesis focuses on delving into the main factors contributing to this gap and exploring strategies to address this challenge. The research outlined in this dissertation is divided into two parts and it combines chemical synthesis and advanced electrochemical characterization to gain deeper insights into parameters governing the charge transfer reaction in organic materials. In the first part, we aim to identify a reliable electrochemical setup conducive to detailed kinetic studies of redox-active organic compounds. We proceed with electrochemical impedance spectroscopy measurements in such a setup, coupled with a combination of microscopy techniques, including focused ion beam scanning electron microscopy (FIB-SEM) and transmission electron microscopy (TEM). This methodology allows us to visualize multivalent ion distribution and evaluate ionic resistances. In the third chapter, we examine the electronic conductivity of organic materials and the implications it has on observed electrochemical performances. The second part of the thesis focuses on chemical synthesis, including miniemulsion polymerization for obtaining nanosized polymers, synthesis of organic polymers with various electronically and ionically conducting fillers, polymers with varying degrees of porosity, and polymers with different lengths of aromatic core and linkers. These efforts aim to assess the influence of structural and morphological factors on electrochemical performance in conjunction with Mg and Ca-based charge carriers. Across four chapters, we validate the applicability of the symmetric cell approach in galvanostatic and impedance investigation of organic polymers, propose a transmission line model elucidating how carbon nanotubes enhance the organic polymer and contribute to improved capacity utilization, develop a methodology for measuring electronic conductivities of polymers reduced in realistic battery conditions, and finally, draw comparisons between different structural and morphological factors affecting capacity utilization in Mg and Ca electrolytes.

• Language: English
• Keywords: redox-active organics, magnesium batteries, calcium batteries, electrochemical impedance spectroscopy, electron microscopy, multivalent ion diffusion
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2024
• PID: 20.500.12556/RUL-159514
• COBISS.SI-ID: 203299331
• Publication date in RUL: 11.07.2024

Secondary language

• Language: Slovenian
• Title: Študij ključnih parametrov pri reakcijah prenosa naboja znotraj organskih katod v multivalentnih akumulatorjih

Abstract

Za učinkovit prehod s fosilnih goriv na obnovljive vire energije je bistven napredek pri shranjevanju električne energije. Pri tem so ključna tehnologija varni ter cenovno ugodni akumulatorji, zato se je povečalo zanimanje za razvoj akumulatorjev, ki temeljijo na novih tehnologijah. Med njimi so posebej zanimivi večvalentni-organski akumulatorji, ki združujejo v naravi bolj pogoste kovine, kot sta magnezij in kalcij, z okolju prijaznimi organskimi katodami. Kljub intenzivnim raziskavam razvoj večvalentnih akumulatorjev še ne dosega stopnje razvoja enovalentnih akumulatorjev, predvsem pri izkoriščanju kapacitete katod. Disertacija obravnava ključne dejavnike, ki vplivajo na razlike v zmogljivosti večvačentnih akumulatorjev na osnovi Mg in Ca, ter raziskuje možne strategije za njihovo reševanje. Raziskave so razdeljene na dva dela in združujejo kemijsko sintezo z elektrokemijsko karakterizacijo za boljše razumevanje parametrov, ki vplivajo na prenos naboja v organskih materialih. Prvi del se osredotoča na iskanje zanesljive elektrokemijske celice za podrobne kinetične študije. Ta del se nadaljuje z meritvami elektrokemijske impedančne spektroskopije v kombinaciji z mikroskopskimi tehnikami, kot sta FIB-SEM in TEM. To nam omogoča vizualizacijo porazdelitve večvalentnih ionov in ocenjevanje ionskih upornosti elektrod ter tudi preučevanje elektronske prevodnosti in njenega vpliva na elektrokemijske lastnosti organskih materialov. Drugi del disertacije se osredotoča na kemijsko sintezo, vključno z mini emulzijsko polimerizacijo za pridobivanje nanodelcev polimerov, sintezo organskih polimerov z različnimi elektronsko in ionsko prevodnimi polnili, polimeri z različnimi stopnjami poroznosti ter polimeri z različnimi dolžinami aromatskega jedra in veznih členov. V tem delu si prizadevamo oceniti vpliv strukturnih in morfoloških dejavnikov na elektrokemijsko delovanje akumulatorske celice z Mg in Ca kot nosilcema naboja. V disertaciji pokažemo uporabnost simetričnih celic pri elektrokemijskem testiranju organskih materialov, predlagamo lestvičasti model (TLM), ki pojasnjuje, kako ogljikova nanovlakna izboljšajo delovanje organskega polimera in prispevajo k izboljšani izkoriščenosti kapacitete, razvijemo metodologijo za merjenje elektronskih prevodnosti reduciranih polimerov med delovanjem akumulatorja, ter izvedemo primerjave med različnimi strukturnimi in morfološkimi aditivi, ki vplivajo na izkoriščenost kapacitete v Mg in Ca elektrolitih.

• Keywords: redoks-aktivne organske spojine, magnezijevi akumulatorji, kalcijevi akumulatorji, elektrokemijska impedančna spektroskopija, elektronska mikroskopija, difuzija multivalentnih ionov