Influence of structural and chemical properties on the electrochemical insertion of sodium into non-graphitizable carbons

Tratnik, Blaž (author), Vižintin, Alen (mentor)

Sodium-ion batteries (SIBs) are the frontrunner to displace lithium-ion batteries (LIBs) in stationary storage applications, due to sodium’s abundance and even distribution around the globe, consequently reducing the strain on lithium resources. Non-graphitizable carbons are currently utilized as negative electrodes in most common SIB configurations, because of their high storage capacities, low cost, and the ability to produce them from waste biomass. However, a general consensus regarding the sodium storage mechanism is yet to be achieved, despite several studies proposing various mechanisms. Moreover, high storage capacities of non-graphitizable carbons still do not satisfy the energy market demands, therefore further improvement of their performance is necessary. This work focused on two aspects of non-graphitizable carbons: the investigation of the sodium storage mechanism, followed by strategies for improvement of charge storage capacities of non-graphitizable carbons. Based on correlations established between the structural evolution at various pyrolysis temperatures and the electrochemical behavior of corncob-derived non-graphitizable carbons, we propose a sodium storage mechanism, endorsing the “adsorption – intercalation – pore filling” model. We demonstrate the effect of the organic precursor on the closed porosity volume of non-graphitizable carbons. Sequential testing with sodium and lithium elucidated the impact of the closed porosity volume on the electrochemical performance. We synthesized a series of heteroatom-doped non-graphitizable carbons to study the influence of introduced heteroatoms on sodium ion diffusivity. Finally, the addition of Bi2S3 nanoparticles on the surface of non-graphitizable carbons was performed to boost the charge storage capacity and improve the cycling stability of non-graphitizable carbons. Based on the employed characterization techniques, we propose a sodium storage mechanism in Bi2S3 nanoparticle decorated non-graphitizable carbons.

• Language: English
• Keywords: sodium-ion batteries, non-graphitizable carbons, sodium storage mechanism, organic precursor, closed porosity, pore filling, heteroatom doping, Bi2S3 nanoparticles
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2023
• PID: 20.500.12556/RUL-147374
• COBISS.SI-ID: 163438339
• Publication date in RUL: 03.07.2023

Secondary language

• Language: Slovenian
• Title: Vpliv strukturnih in kemijskih lastnosti na elektrokemijsko vgradnjo natrija v negrafitizirane ogljike

Abstract

Na-ion akumulatorji so glavni kandidat za zamenjavo Li-ion akumulatorjev v stacionarnih aplikacijah za shranjevanje energije, zaradi obilnih nahajališč natrija, kar posledično zmanjšuje obremenitev virov litija. Negrafitizirani ogljiki se uporabljajo kot negativne elektrode v Na-ion akumulatorjih zaradi visokih zmogljivosti shranjevanja naboja, nizke cene in možnosti proizvodnje iz odpadne biomase. Vendar pa splošno soglasje glede mehanizma shranjevanja natrija še ni bilo doseženo, kljub temu da je bilo v študijah predlaganih več različnih mehanizmov. Poleg tega visoke zmogljivosti shranjevanja naboja negrafitiziranih ogljikov še vedno ne zadovoljujejo zahtev energetskega trga, zato je potrebno njihovo delovanje še izboljšati. To delo se osredotoča na dva vidika negrafitiziranih ogljikov: raziskavo mehanizma shranjevanja natrija, čemur sledijo strategije za izboljšanje zmogljivosti shranjevanja naboja v negrafitiziranih ogljikih. Na podlagi korelacij med razvojem strukture pri različnih temperaturah pirolize in elektrokemijskim delovanjem negrafitiziranih ogljikov, pridobljenih iz koruznega storža, smo predlagali mehanizem shranjevanja natrija, ki podpira model "adsorpcija - interkalacija - polnjenje por". Dokazali smo vpliv organskega prekurzorja na prostornino zaprte poroznosti negrafitiziranih ogljikov. Zaporedno testiranje z natrijem in litijem je pojasnilo vpliv zaprte poroznosti na elektrokemijsko delovanje. Sintetizirali smo vrsto negrafitiziranih ogljikov dopiranih s heteroatomi, za preučitev vpliva vnesenih heteroatomov na difuzivnost natrijevih ionov. Na koncu smo z dodatkom Bi2S3 nanodelcev na površino negrafitiziranih ogljikov povečali kapaciteto shranjevanja naboja in izboljšali stabilnost delovanja negrafitiziranih ogljikov. Na podlagi uporabljenih tehnik karakterizacije smo predlagali mehanizem shranjevanja natrija v negrafitiziranih ogljikih, okrašenih z Bi2S3 nanodelci.

• Keywords: Na-ion akumulatorji, negrafitizirani ogljiki, mehanizem shranjevanja natrija, organski prekurzorji, zaprta poroznost, polnjenje por, dopiranje s heteroatomi, Bi2S3 nanodelci