start-ver=1.4 cd-journal=joma no-vol=225 cd-vols= no-issue= article-no= start-page=137 end-page=140 dt-received= dt-revised= dt-accepted= dt-pub-year=2013 dt-pub=201303 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=NMR study for electrochemically inserted Na in hard carbon electrode of sodium ion battery en-subtitle= kn-subtitle= en-abstract= kn-abstract=The state of sodium inserted in the hard carbon electrode of a sodium ion battery having practical cyclability was investigated using solid state 23Na NMR. The spectra of carbon samples charged (reduced) above 50 mAh g−1 showed clear three components. Two peaks at 9.9 ppm and 5.2 ppm were ascribed to reversible sodium stored between disordered graphene sheets in hard carbon because the shift of the peaks was invariable with changing strength of external magnetic field. One broad signal at about −9 to −16 ppm was assigned to sodium in heterogeneously distributed closed nanopores in hard carbon. Low temperature 23Na static and magic angle spinning NMR spectra didn't split or shift whereas the spectral pattern of 7Li NMR for lithium-inserted hard carbon changes depending on the temperature. This strongly suggests that the exchange of sodium atoms between different sites in hard carbon is slow. These studies show that sodium doesn't form quasi-metallic clusters in closed nanopores of hard carbon although sodium assembles at nanopores while the cell is electrochemically charged. en-copyright= kn-copyright= en-aut-name=GotohKazuma en-aut-sei=Gotoh en-aut-mei=Kazuma kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=IshikawaToru en-aut-sei=Ishikawa en-aut-mei=Toru kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=ShimadzuSaori en-aut-sei=Shimadzu en-aut-mei=Saori kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=YabuuchiNaoaki en-aut-sei=Yabuuchi en-aut-mei=Naoaki 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=TakedaKazuyuki en-aut-sei=Takeda en-aut-mei=Kazuyuki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= en-aut-name=GotoAtsushi en-aut-sei=Goto en-aut-mei=Atsushi 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=HashiKenjiro en-aut-sei=Hashi en-aut-mei=Kenjiro kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=10 ORCID= en-aut-name=ShimizuTadashi en-aut-sei=Shimizu en-aut-mei=Tadashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=11 ORCID= en-aut-name=IshidaHiroyuki en-aut-sei=Ishida en-aut-mei=Hiroyuki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=12 ORCID= affil-num=1 en-affil= kn-affil=Graduate School of Natural Science & Technology, Okayama University affil-num=2 en-affil= kn-affil=Department of Applied Chemistry, Tokyo University of Science affil-num=3 en-affil= kn-affil=Department of Applied Chemistry, Tokyo University of Science affil-num=4 en-affil= kn-affil=Department of Applied Chemistry, Tokyo University of Science affil-num=5 en-affil= kn-affil=Department of Applied Chemistry, Tokyo University of Science affil-num=6 en-affil= kn-affil=Division of Chemistry, Graduate School of Science, Kyoto University affil-num=7 en-affil= kn-affil=National Institute for Materials Science affil-num=8 en-affil= kn-affil=National Institute for Materials Science affil-num=9 en-affil= kn-affil=National Institute for Materials Science affil-num=10 en-affil= kn-affil=National Institute for Materials Science affil-num=11 en-affil= kn-affil=National Institute for Materials Science affil-num=12 en-affil= kn-affil=Graduate School of Natural Science & Technology, Okayama University en-keyword=Sodium ion battery kn-keyword=Sodium ion battery en-keyword=Anode kn-keyword=Anode en-keyword=Hard carbon kn-keyword=Hard carbon en-keyword=23Na kn-keyword=23Na en-keyword=Solid state NMR kn-keyword=Solid state NMR END 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