Experimental Mn and Ni K-edge X-ray absorption near-edge structure (XANES) spectra were well reproduced for 5 V-class LixNi0.5Mn1.5O4 spinels as well as 4 V-class LixMn2O4 spinels using density functional theory. Local environmental changes around the Mn or Ni centres due to differences in the locations of Li ions and/or phase transitions in the spinel oxides were found to be very important contributors to the XANES shapes, in addition to the valence states of the metal ions.

•All-solid-state lithium-ion batteries were assembled using a Li2.2C0.8B0.2O3 electrolyte.•Reversible charge–discharge profile of LiCoO2 was observed.•Large repetitive expansion–contraction of the electrode affects fatigue failure.Oxide-based all-solid-state lithium-ion battery is prepared by a conventional sintering process, thanks to the intrinsic low melting point of Li2.2C0.8B0.2O3. A well-defined interface between LiCoO2 and Li2.2C0.8B0.2O3 was confirmed without any traces of impurities. Li ion reversibly (de-)intercalated from/into LiCoO2 at initial charge–discharge process when the charge capacity was limited to 120 mAh g− 1. The capacity degradation after subsequent cycling was suppressed by further limitation of the charging capacity. However, capacity fade could still be confirmed after 20 cycles albeit the capacity was limited at 60 mAh g− 1. This study suggests large repetitive expansion–contraction of the electrode during cycling as a possible cause of fatigue failure of the electrode/oxide electrolyte interface.

The cobalt-based fluorophosphate Li2CoPO4F positive electrode has the potential to obtain high energy density in a lithium ion battery since its theoretical capacity is 287 mAh·g–1 when two electrons can react reversibly. This material promises to charge/discharge with an extremely high redox-couple voltage of over 4.8 V vs Li/Li+. Bulk structural analyses including X-ray diffraction, Co K-edge X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal that an orthorhombic LiβCoPO4F phase is produced from pristine Li2CoPO4F by a combination of solid-solution and two-phase reaction manners during the first charging process, and these phases reversibly transform during charge–discharge cycling. The results of 7Li MAS NMR and classical molecular dynamics simulations suggest that Li ions located at Li(1) sites intercalate/deintercalate through a 1D diffusion path along the b axis, whereas those located at Li(2) and Li(3) sites are fixed. The aforementioned analyses were successfully performed with the enhancement of electrochemical properties by use of a fluoroethylene carbonate-based electrolyte instead of an ethylene carbonate-based one and reducing its volume. Further enhancement was achieved by adding SiO2 nanoparticles into the electrode slurry. The electrochemical results encourage the possibility of the intercalation/deintercalation of more than one Li ion from/into Li2CoPO4F during electrochemical cycling.

Bulk and surface structural changes induced in a Li5FeO4 positive electrode with a defect anti-fluorite type structure are examined during its initial charge–discharge cycle by various synchrotron-radiation analysis techniques, with a view to determining the contribution of oxygen to its electrochemical properties. Bulk structural analyses including XRD, Fe K-edge XANES and EXAFS reveal that pseudo-cubic lithium iron oxides (PC-LFOs), in the form of LiαFe(4−α)+O2, are formed during the first charging process instead of the decomposition of pristine Li5FeO4. Moreover, the relative volume of this PC-LFO phase varies nonlinearly according to the charging depth. At the same time, the surface lithium compounds such as Li2O cover over the PC-LFO phase, which also contribute to the overall electrochemical reaction, as measured from the O K-edge XANES operating in a surface-sensitive total-electron yield mode. The ratio of these two different reaction mechanisms changes with the depth during the first charging process, with this tendency causing variation in the subsequent discharge capacity retention in relation to the depth of the charging electron and/or temperature of this “Li-rich” positive electrode. Indeed, such behaviour is noted to be very similar to the specific electrochemical properties of Li2MnO3.

X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides LixMn2O4 (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn2O4 models, the contributions of the Mn3+ ion and Mn4+ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn3+Mn4+)O4 and de-intercalated Li0.5(Mn3+0.5Mn4+1.5)O4 and Mn4+2O4 (λ-MnO2). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn2O4 to tetragonal I41/amd Li2Mn2O4) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.

The electronic structural changes during lithium-ion intercalation/de-intercalation process of nickel substituted lithium manganese spinel oxides have been investigated by using X-ray absorption near-edge structure (XANES) spectra of O K-edges as well as Ni L3-edges and Mn L3-edges. The results of the XANES spectra indicate that the electronic structure of both manganese and oxygen atoms contribute on the redox reaction at 0.06 ≤ x < 1, and only that of nickel atom affect the redox reaction at 1 < x ≤ 1.78 in LixNi0.5Mn1.5O4. Thus, the electronic structural change of oxygen atom is also crucial for considering redox reaction at intercalation/de-intercalation process, and the contribution of the oxygen atom on redox reaction differs in various redox cation species.Highlights► Soft XANES techniques reveal the change of hybridized LUMO in LixNi0.5Mn1.5O4. ► Electronic structure of O is crucial for considering redox reaction of batteries. ► Contribution of the O on redox reaction differs in various cation species.

First-principle calculation was employed to simulate X-ray absorption near-edge structure (XANES) spectroscopy of two typical types of lithium cobalt oxides to clarify the electronic and local structural changes during lithium-ion de-intercalation. The simulated Co K-edge XANES spectra agreed well with the observed spectra. The differences in the shape of the XANES spectra with structural symmetry and/or lithium contents in lithium cobalt oxides were analyzed based on the partial density of state (PDOS) of the excited energy level. First-principle calculation simulations revealed that the cobalt PDOS overlapped with nearby lithium PDOS via oxygen PDOS, and the overlap difference among various Li1−xCoO2 could be detected using both the experimental and theoretical Co K-edge XANES spectra.

Experimental Mn and Ni K-edge X-ray absorption near-edge structure (XANES) spectra were well reproduced for 5 V-class LixNi0.5Mn1.5O4 spinels as well as 4 V-class LixMn2O4 spinels using density functional theory. Local environmental changes around the Mn or Ni centres due to differences in the locations of Li ions and/or phase transitions in the spinel oxides were found to be very important contributors to the XANES shapes, in addition to the valence states of the metal ions.

First-principle calculation was employed to simulate X-ray absorption near-edge structure (XANES) spectroscopy of two typical types of lithium cobalt oxides to clarify the electronic and local structural changes during lithium-ion de-intercalation. The simulated Co K-edge XANES spectra agreed well with the observed spectra. The differences in the shape of the XANES spectra with structural symmetry and/or lithium contents in lithium cobalt oxides were analyzed based on the partial density of state (PDOS) of the excited energy level. First-principle calculation simulations revealed that the cobalt PDOS overlapped with nearby lithium PDOS via oxygen PDOS, and the overlap difference among various Li1−xCoO2 could be detected using both the experimental and theoretical Co K-edge XANES spectra.

Bulk and surface structural changes induced in a Li5FeO4 positive electrode with a defect anti-fluorite type structure are examined during its initial charge–discharge cycle by various synchrotron-radiation analysis techniques, with a view to determining the contribution of oxygen to its electrochemical properties. Bulk structural analyses including XRD, Fe K-edge XANES and EXAFS reveal that pseudo-cubic lithium iron oxides (PC-LFOs), in the form of LiαFe(4−α)+O2, are formed during the first charging process instead of the decomposition of pristine Li5FeO4. Moreover, the relative volume of this PC-LFO phase varies nonlinearly according to the charging depth. At the same time, the surface lithium compounds such as Li2O cover over the PC-LFO phase, which also contribute to the overall electrochemical reaction, as measured from the O K-edge XANES operating in a surface-sensitive total-electron yield mode. The ratio of these two different reaction mechanisms changes with the depth during the first charging process, with this tendency causing variation in the subsequent discharge capacity retention in relation to the depth of the charging electron and/or temperature of this “Li-rich” positive electrode. Indeed, such behaviour is noted to be very similar to the specific electrochemical properties of Li2MnO3.

X-ray absorption near-edge structure (XANES) spectroscopy, which reveals the features of the electronic and local structure, of lithium manganese oxides LixMn2O4 (x = 0–2) was examined using first-principles calculations. Both the easily observable parts and the tiny peaks of the theoretical Mn K-edge XANES spectra agreed with the experimental spectra. From the theoretical results of two anti-ferromagnetic LiMn2O4 models, the contributions of the Mn3+ ion and Mn4+ ion centers to the XANES spectra differ due to the difference in the overlap between the Mn 4p partial density of state (PDOS) and the O 2p PDOS. Similar results can be also seen by comparing the theoretical XANES spectra and the PDOS between Li(Mn3+Mn4+)O4 and de-intercalated Li0.5(Mn3+0.5Mn4+1.5)O4 and Mn4+2O4 (λ-MnO2). The XANES spectral changes with the lithium ion displacement (six- to four-coordination) due to the phase transition (cubic Fdm LiMn2O4 to tetragonal I41/amd Li2Mn2O4) can be determined by the indirect contribution of the Li 2p PDOS to the Mn 4p PDOS via the O 2p PDOS.