DFT Modeling of NMR Contact Shift Mechanism in the Ideal LiNi2O4 Spinel and Application to Thermally Treated Layered Li0.5NiO2
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- 作者：Cé ; dric Chazel ; Michel Mé ; né ; trier ; Dany Carlier ; Laurence Croguennec ; Claude Delmas
- 刊名：Chemistry of Materials
- 出版年：2007
- 出版时间：August 21, 2007
- 年：2007
- 卷：19
- 期：17
- 页码：4166 - 4173
- 全文大小：304K
- 年卷期：v.19,no.17(August 21, 2007)
- ISSN：1520-5002
文摘
LiNi2O4 spinel-type phases were prepared by thermal treatment of electrochemically deintercalatedlayered Li~0.5NiO2. The phase transformation was followed by 7Li NMR, showing a gradual change ofthe signal from the layered compound. The characteristic signal of the latter (related to local Li/vacancyand Ni3+/Ni4+ ordering) vanishes after heating to 150 
ntities/deg.gif">C and is replaced by a new signal showing fasterexchange kinetics (originating from Ni3+/Ni4+ hopping around Li), which progressively transforms intoa broad distribution of signals. Around 200 ntities/deg.gif">C, a set of three positively shifted signals is observed,corresponding to the appearance of the spinel phase as seen from XRD; these signals disappear afterheating to 240 ntities/deg.gif">C, corresponding to the beginning of decomposition of the spinel into a disordered Rntities/thremacr.gif">mtype phase with oxygen evolution as previously shown by Guilmard et al. (Chem. Mater. 2003, 15, 4476and 4484). In an ideal LiNi2O4 spinel, only one 7Li NMR signal is expected. DFT (GGA) calculationswere carried out and show that the mechanism for the electron spin density transfer from NiO6 octahedrato corner-sharing LiO4 tetrahedra with close to 120ntities/deg.gif"> Ni-O-Li configuration is a delocalization one,although the p orbitals on oxygen do not present ideal orientation, leading to a much weaker transfercompared to cases where both Ni and Li are in octahedral coordination with 180ntities/deg.gif"> Ni-O-Li configuration.The complex but well-defined experimental NMR signals consistently observed show that the materialis far from the ideal spinel structure. However, it could not be correlated to the actual stoichiometry ofthe compound. It was therefore tentatively assigned to structural defects resulting from incomplete migrationof Ni ions from their site to the Li layer in the pristine compound, such as partial occupation of tetrahedralsites.
ntities/deg.gif">C and is replaced by a new signal showing fasterexchange kinetics (originating from Ni3+/Ni4+ hopping around Li), which progressively transforms intoa broad distribution of signals. Around 200 ntities/deg.gif">C, a set of three positively shifted signals is observed,corresponding to the appearance of the spinel phase as seen from XRD; these signals disappear afterheating to 240 ntities/deg.gif">C, corresponding to the beginning of decomposition of the spinel into a disordered Rntities/thremacr.gif">mtype phase with oxygen evolution as previously shown by Guilmard et al. (Chem. Mater. 2003, 15, 4476and 4484). In an ideal LiNi2O4 spinel, only one 7Li NMR signal is expected. DFT (GGA) calculationswere carried out and show that the mechanism for the electron spin density transfer from NiO6 octahedrato corner-sharing LiO4 tetrahedra with close to 120ntities/deg.gif"> Ni-O-Li configuration is a delocalization one,although the p orbitals on oxygen do not present ideal orientation, leading to a much weaker transfercompared to cases where both Ni and Li are in octahedral coordination with 180ntities/deg.gif"> Ni-O-Li configuration.The complex but well-defined experimental NMR signals consistently observed show that the materialis far from the ideal spinel structure. However, it could not be correlated to the actual stoichiometry ofthe compound. It was therefore tentatively assigned to structural defects resulting from incomplete migrationof Ni ions from their site to the Li layer in the pristine compound, such as partial occupation of tetrahedralsites.