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Modification of lithium surface for batteries applications
Bobnar, Jernej (Author), Genorio, Boštjan (Mentor) More about this mentor... This link opens in a new window, Dominko, Robert (Co-mentor)

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Abstract
Increasing global energy demand requires high energy density batteries for which the replacement of intercalation or conversion anodes with lithium metal is a crucial step towards batteries with improved energy density. State-of-the-art secondary lithium metal batteries still suffer from low Coulombic efficiency and low safety related to the thermodynamically unstable solid electrolyte interphase (SEI) between metallic lithium and the electrolyte in most of the liquid electrolytes, resulting in high surface area lithium (HSAL) growth. Various approaches can be used to suppress HSAL formation, including protective layer preparation on the lithium surface. Properties of the protective layer should be high Li-ion conductivity, electronic resistivity, small thickness, and high Young’s modulus to withstand the applied stress during lithium stripping and the deposition process within the cell. In this work, we investigated three different approaches employed as a protective layer on a lithium surface to suppress HSAL growth. The protective layers were examined with electrochemical measurements supported by scanning electron microscopy, X-ray photoelectron spectroscopy, and other techniques. We demonstrate that the functionalization of graphene modifies its electronic and ionic properties to make it suitable for use in protective layer applications. The impact of graphene oxide (GO), reduced graphene oxide (rGO), and fluorinated reduced graphene oxide (FG) as protective layers on a lithium surface on HSAL growth suppression was studied in Li symmetric cells. Additionally, the FG protective nature was evaluated in two full cell configurations (Li-ion and Li-sulfur) in carbonate and ether-based electrolyte. The physical characteristics and electrochemical measures had shown the dual role of the FG protective layer. First, it acts as a Li-ion conductive layer and electronic insulator on metallic lithium surface; second, it successfully suppresses dendritic growth. Enhanced electrochemical performance of the full cell battery system indicates potential applications in the secondary lithium metal batteries of the future. Metal fluorides (MgF2and AlF3) were studied as precursors of protective layerson a lithium surface. The use of MgF2-modified lithium resulted in denser lithium deposits, enhanced stability in symmetric cells and prolonged cycling in Li-sulfur batteries with fluorinated electrolyte. Finally, the in-situ anionic polymerization of trimethylolpropane ethoxylate triacrylate on a lithium surface resulted in completely hindered lithium ion transport through the layer and exposure of the edge effect. Correspondingly, we designed a new cell configuration that enables more accurate electrochemical evaluation of protective layerswith edge effect avoidance.

Language:English
Keywords:Li-sulfur batteries, Li metal batteries, artificial SEI, protective layer, dendrite growth suppression, graphene oxide, reduced graphene oxide, fluorinated reduced graphene oxide, metal fluoride, anionic polymerization, trimethylolpropane ethoxylate triacrylate, edge effect
Work type:Doctoral dissertation (mb31)
Tipology:2.08 - Doctoral Dissertation
Organization:FKKT - Faculty of Chemistry and Chemical Technology
Year:2019
COBISS.SI-ID:303218176 This link opens in a new window
Views:713
Downloads:238
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Secondary language

Language:Slovenian
Title:Modifikacija površine litija za akumulatorske aplikacije
Abstract:
Povečana svetovna poraba energije kliče po razvoju novih akumulatorjev z visoko energijsko gostoto. Zamenjava interkalacijskih oziroma konverzijskih anod s kovinskim litijem je zato ključni korak pri razvoju akumulatorjev z izboljšano energijsko gostoto. Najsodobnejši akumulatorji s kovinskim litijem so trenutno še v razvoju, predvsem zaradi težav z nizko Coulombsko učinkovitostjo in pomanjkljivo varnostjo, ki je posledica prisotnosti termodinamsko nestabilnega pasivnega sloja elektrolita na medfazni meji (SEI) kovinski litij/elektrolit. Nestabilen SEI se tvori v večini tekočih elektrolitov, kar vodi do tvorbe visoko površinskega litija (HSAL). Proti nastanku tvorbe HSAL lahko uporabimo različne pristope, vključno s pripravo zaščitnega sloja na litijevi površini. Zaščitni sloj mora biti visoko Li-ionsko prevoden, elektronsko neprevoden, hkrati pa mora biti čim tanjši in z visokim modulom elastičnosti, da lahko prenese stres, ki se pojavi med elektrokemijskim jedkanjem in odlaganjem litija znotraj celice. V doktorskem delu smo raziskali tri različne pristope, ki smo jih uporabili kot zaščitni sloj na litijevi površini, da bi preprečili rast HSAL. Zaščitne sloje smo okarkaterizirali z elektrokemijskimi meritvami, z uporabo vrstične elektronske mikroskopije in rentgenske foto-elektronske spektroskopije ter z drugimi tehnikami. Pokazali smo, da lahko s funkcionalizacijo grafena krojimo njegove elektronske in ionske lastnosti, kar posledično omogoča uporabo v aplikacijah zaščitnega sloja. V litijevi simetrični celici smo proučevali vpliv grafen oksida (GO), reduciranega grafen oksida (rGO) in fluoriranega reduciranega grafen oksida (FG) kot zaščitnega sloja na litijevi površini za preprečevanje rasti HSAL. Poleg tega smo delovanje FG zaščitnega sloja ovrednotili tudi v Li-ionskem in Li-žveplovem akumulatorju v karbonatnih in etrskih elektrolitih. Fizikalne lastnosti in elektrokemijske meritve so pokazale dvojno vlogo FG zaščitnega sloja. Prvič deluje kot Li-ionski prevodnik in hkrati elektronski izolator na površini kovinskega litija in drugič uspešno zavira rast HSAL. Izboljšana elektrokemijska zmogljivost akumulatorja z FG zaščitenim litijem kaže na potencialno uporabo v modernih akumulatorjih z visoko energijsko gostoto. Kovinska fluorida (MgF2in AlF3) smo preučevali kot prekurzorja za tvorbo zaščitnega sloja na litijevi površini. Uporaba litija z MgF2 modificirano površino je vodila do nastajanja gostejših litijevih depozitov, povečane stabilnosti v litij simetrični celici in podaljšano življenjsko dobo Li-žveplovega akumulatorja s fluoriranimi elektroliti. In-situ anionska polimerizacija trimetilolpropan etoksilat triakrilata na litijevi površini je povzročila popolnoma blokiran Li-ionski transport skozi zaščitni sloj, kar je posledično izpostavilo t.i. »robni efekt«. V ta namen smo oblikovali novo konfiguracijo celice, ki je omogočila natančnejše elektrokemijsko vrednotenje zaščitnega sloja brez vpliva »robnega efekta«.

Keywords:Li-žveplovi akumulatorji, akumulatorji s kovinskim litijem, umetni SEI, zaščitni sloj, preprečitev dendritske rasti, grafen oksid, reduciran grafen oksid, fluoriran reduciran grafen oksid, kovinski fluorid, anionska polimerizacija, trimetilolpropan etoksilat triakrilat, robni efekt

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