20.500.12556/RUL-178803 Študija delovanja ogljikovih elektrod v novodobnih akumulatorskih sistemih z jedrsko magnetno resonanco Study of the Operation of Carbon Electrodes in Modern Battery Systems by Nuclear Magnetic Resonance Natrij-ionski akumulatorji (NIB-i) so zaradi manjšega vpliva na okolje, večje varnosti in konkurenčne gostote energije privlačna alternativa litij-ionskim (LIB-i). Ključni dejavnik pri izboljšanju teh akumulatorjev je izbira negativnega elektrodnega materiala, ki pomembno vpliva na zmogljivost, stabilnost in nastanek fazne meje trdno-elektrolit (SEI). Trdi oziroma negrafitizirani ogljiki so postali glavni kandidati negativnega elektrodnega materiala za NIB. V zadnjih raziskavah je veliko pozornosti pritegnil proces vnosa Na$^+$ ionov v/iz negrafitiziranih ogljikov. Ker gre za razmeroma novo tehnologijo v primerjavi z LIB-i, natančen mehanizem delovanja in poti degradacije NIB-ov ostajajo nedorečeni. V doktorskem delu raziskujem mehanizme shranjevanja natrija v negativnih elektrodah iz negrafitiziranega ogljika z uporabo naprednih karakterizacijskih tehnik. Poleg uporabe operando, in-situ in ex-situ jedrske magnetne resonančne (NMR) spektroskopije v trdnem so bile uporabljene tudi vrstična elektronska mikroskopija z energijsko-disperzijsko rentgensko spektroskopijo (SEM-EDX), rentgenska fotoelektronska spektroskopija (XPS) in elektrokemijske meritve. Te metode so omogočile vpogled v natrijevo strukturo, dinamiko in sestavo SEI-ja. Ključne ugotovitve vključujejo vpliv temperature karbonizacije na shranjevanje natrija. Pri višjih temperaturah večje pore olajšajo nastanek kvazi-kovinskih natrijevih skupkov, kar izboljša zmogljivost shranjevanja natrija. Poleg tega je bilo ugotovljeno, da je SEI sestavljen iz natrijevega fluorida (NaF), ki se tvori na površini negrafitiziranega ogljika, znotraj plasti pa se tvori natrijev karbonat (Na$_2$CO$_3$). Predlagan je bil celovit mehanizem za obnašanje Na$^+$ ionov v negrafitiziranem ogljiku: med začetnim sodiiranjem se Na$^+$ ioni adsorbirajo na površini negrafitiziranega ogljika in vstavijo med plasti grafena, nato zapolnijo stene por, na koncu pa, če so pore dovolj velike, nastanejo kvazi-kovinski Na skupki. Med desodiiranjem se ta proces obrne. V primeru podpotencialne sodiacije pride do nukleacije kovinskega Na na površini negativne elektrode, kar povzroči kovinsko nanašanje Na. Kemijska okolja nanešenega Na in Na dendritov se razlikujejo zaradi različnih strukturnih in kemijskih lastnosti in jih je mogoče razlikovati z NMR v trdnem stanju. Negativno elektrodo iz negrafitiziranega ogljika sem testiral skupaj s pozitivno elektrodo iz Na$_3$V$_2$(PO$_4$)$_2$F$_3$ z operando NMR-jem tudi v polnem členu in tako pokazal delovanje akumulatorja pri realnih pogojih. S pomočjo ex-situ NMR-ja sem dodatno raziskal vpliv dodatka FEC v elektrolitu na formiranje in stabilizacijo SEI-ja. Na koncu sem s pomočjo ex-situ in operando NMR-ja raziskal vpliv heteroatomskega dekoriranja negrafitiziranega ogljika z nanodelci in vpliv uporabe različnih prekurzorjev na delovanje in degradacijske mehanizme akumulatorja. Sodium-ion batteries (NIBs) are an attractive alternative to lithium-ion batteries (LIBs) due to their lower environmental impact, greater safety, and competitive energy density. A key factor in improving these batteries is the choice of negative electrode material, which significantly affects performance, stability, and the formation of the solid electrolyte interphase (SEI). Hard or non-graphitized carbons have become the main candidates for negative electrode materials for NIBs. In recent research, the process of Na$^+$ ion insertion into/from non-graphitized carbons has attracted a lot of attention. As this is a relatively new technology compared to LIBs, the exact mechanism of action and degradation pathways of NIBs remain unclear. In my doctoral thesis, I am investigating the mechanisms of sodium storage in non-graphitized carbon negative electrodes using advanced characterization techniques. In addition to operando, in-situ, and ex-situ nuclear magnetic resonance (NMR) spectroscopy in the solid-state, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were also used. These methods provided insights into the sodium structure, dynamics, and composition of SEI. Key findings include the effect of carbonization temperature on sodium storage. At higher temperatures, larger pores facilitate the formation of quasi-metallic sodium clusters, which improves sodium storage capacity. In addition, it was found that the SEI consists of sodium fluoride (NaF) formed on the surface of the non-graphitized carbon, while sodium carbonate (Na$_2$CO$_3$) forms within the layers. A comprehensive mechanism for the behaviour of Na$^+$ ions in non-graphitized carbon was proposed: during initial sodiation, Na$^+$ ions are adsorbed on the surface of non-graphitized carbon and inserted between graphene layers, then fill the pore walls, and finally, if the pores are large enough, quasi-metallic Na clusters are formed. During desodiation, this process is reversed. In the case of underpotential sodiation, metal Na nucleates on the surface of the negative electrode, causing metal Na plating. The chemical environments of the plated Na and Na dendrites differ due to their different structural and chemical properties and can be distinguished by solid-state NMR. I tested the negative electrode made of non-graphitized carbon together with the positive electrode made of Na$_3$V$_2$(PO$_4$)$_2$F$_3$ using operando NMR in a full cell, thus demonstrating the battery's performance under real conditions. Using ex-situ NMR, I further investigated the effect of FEC addition in the electrolyte on SEI formation and stabilization. Finally, using ex-situ and operando NMR, I investigated the effect of heteroatom decoration of non-graphitized carbon with nanoparticles and the impact of the use of different precursors on the performance and degradation mechanisms of the battery. jedrska magnetna resonanca operando meritve natrij-ionski akumulatorji negrafitizirani ogljiki mehanizem shranjevanja natrija degradacija organski prekurzorji polnjenje por dekoriranje z nanodelci nuclear magnetic resonance operando measurements sodium-ion batteries non-graphitizable carbons sodium storage mechanism degradation organic precursor pore filling nanoparticle decoration true false false Slovenski jezik Angleški jezik Doktorsko delo/naloga 2026-01-30 08:15:27 2026-01-30 08:15:35 2026-02-04 12:09:19 0000-00-00 00:00:00 2026 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 159233 267275011 21157.pdf 21157.pdf 1 4377F0298BAC2C022AEAABE5FEB6D47A 65c7040ff665047317508d7738f076e1395b71943e19e324bdb2c9788613d5b2 6e7f6957-fdab-11f0-a1ba-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=226785 Fakulteta za matematiko in fiziko 0 0 0