start-ver=1.4 cd-journal=joma no-vol=4 cd-vols= no-issue=34 article-no= start-page=13183 end-page=13193 dt-received= dt-revised= dt-accepted= dt-pub-year=2016 dt-pub=20160725 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Combination of solid state NMR and DFT calculation to elucidate the state of sodium in hard carbon electrodes en-subtitle= kn-subtitle= en-abstract= kn-abstract=We examined the state of sodium electrochemically inserted in HC prepared at 700?2000 °C using solid state Na magic angle spinning (MAS) NMR and multiple quantum (MQ) MAS NMR. The 23Na MAS NMR spectra of Na-inserted HC samples showed signals only in the range between +30 and ?60 ppm. Each observed spectrum was ascribed to combinations of Na+ ions from the electrolyte, reversible ionic Na components, irreversible Na components assigned to solid electrolyte interphase (SEI) or non-extractable sodium ions in HC, and decomposed Na compounds such as Na2CO3. No quasi-metallic sodium component was observed to be dissimilar to the case of Li inserted in HC. MQMAS NMR implies that heat treatment of HC higher than 1600 °C decreases defect sites in the carbon structure. To elucidate the difference in cluster formation between Na and Li in HC, the condensation mechanism and stability of Na and Li atoms on a carbon layer were also studied using DFT calculation. Na3 triangle clusters standing perpendicular to the carbon surface were obtained as a stable structure of Na, whereas Li2 linear and Li4 square clusters, all with Li atoms being attached directly to the surface, were estimated by optimization. Models of Na and Li storage in HC, based on the calculated cluster structures were proposed, which elucidate why the adequate heat treatment temperature of HC for high-capacity sodium storage is higher than the temperature for lithium storage. en-copyright= kn-copyright= en-aut-name=MoritaRyohei en-aut-sei=Morita en-aut-mei=Ryohei kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=GotohKazuma en-aut-sei=Gotoh en-aut-mei=Kazuma kn-aut-name=後藤和馬 kn-aut-sei=後藤 kn-aut-mei=和馬 aut-affil-num=2 ORCID= en-aut-name=FukunishiMika en-aut-sei=Fukunishi en-aut-mei=Mika kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=KubotaKei en-aut-sei=Kubota en-aut-mei=Kei kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=KomabaShinichi en-aut-sei=Komaba en-aut-mei=Shinichi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=NishimuraNaoto en-aut-sei=Nishimura en-aut-mei=Naoto kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= en-aut-name=YumuraTakashi en-aut-sei=Yumura en-aut-mei=Takashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=7 ORCID= en-aut-name=DeguchiKenzo en-aut-sei=Deguchi en-aut-mei=Kenzo kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=8 ORCID= en-aut-name=OhkiShinobu en-aut-sei=Ohki en-aut-mei=Shinobu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=9 ORCID= en-aut-name=ShimizueTadashi en-aut-sei=Shimizue en-aut-mei=Tadashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=10 ORCID= en-aut-name=IshidaHiroyuki en-aut-sei=Ishida en-aut-mei=Hiroyuki kn-aut-name=石田祐之 kn-aut-sei=石田 kn-aut-mei=祐之 aut-affil-num=11 ORCID= affil-num=1 en-affil=Graduate School of Natural Science & Technology, Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Natural Science & Technology, Okayama University kn-affil=岡山大学大学院自然科学研究科 affil-num=3 en-affil=Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University kn-affil= affil-num=4 en-affil=Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University kn-affil= affil-num=5 en-affil=Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University kn-affil= affil-num=6 en-affil=Department of Chemistry and Materials Technology, Kyoto Institute of Technology kn-affil= affil-num=7 en-affil=Department of Chemistry and Materials Technology, Kyoto Institute of Technology kn-affil= affil-num=8 en-affil=National Institute for Materials Science kn-affil= affil-num=9 en-affil=National Institute for Materials Science kn-affil= affil-num=10 en-affil=National Institute for Materials Science kn-affil= affil-num=11 en-affil=Graduate School of Natural Science & Technology, Okayama University kn-affil=岡山大学大学院自然科学研究科 END