The atomic and electronic structures of binary Li2S-P2S5 glasses used as solid electrolytes are modeled by a combination of density functional theory (DFT) and reverse Monte Carlo (RMC) simulation using synchrotron X-ray diffraction, neutron diffraction, and Raman spectroscopy data. The ratio of PSx polyhedral anions based on the Raman spectroscopic results is reflected in the glassy structures of the 67Li2S-33P2S5, 70Li2S-30P2S5, and 75Li2S-25P2S5 glasses, and the plausible structures represent the lithium ion distributions around them. It is found that the edge sharing between PSx and LiSy polyhedra increases at a high Li2S content, and the free volume around PSx polyhedra decreases. It is conjectured that Li+ ions around the face of PSx polyhedra are clearly affected by the polarization of anions. The electronic structure of the DFT/RMC model suggests that the electron transfer between the P ion and the bridging sulfur (BS) ion weakens the positive charge of the P ion in the P2S7 anions. The P2S7 anions of the weak electrostatic repulsion would causes it to more strongly attract Li+ ions than the PS4 and P2S6 anions, and suppress the lithium ionic conduction. Thus, the control of the edge sharing between PSx and LiSy polyhedra without the electron transfer between the P ion and the BS ion is expected to facilitate lithium ionic conduction in the above solid electrolytes.

The layered-to-spinel phase transformation in Li2MnO3 during the initial charge process occurs by a two-phase reaction process within a single particle.

To examine the dynamical origin of high ionic conductivity of (Li2S)70(P2S5)30 glass ceramic obtained by annealing (Li2S)70(P2S5)30 glass, we applied 6/7Li and 31P solid-state NMR. NMR line shapes and spin–lattice relaxation times (T 1) were measured as a function of temperature. The results showed that dynamics of the PS4 tetrahedra and P2S7 ditetrahedra units in (Li2S)70(P2S5)30 glass ceramic is not appreciable at temperatures below ca. 310 K, where the ionic conductivity is low. At higher temperatures, however, significant motion especially for the P2S7 ditetrahedra unit is apparent in both of 31P-T 1 and 31P MAS line shapes. Further, we applied the 31P–31P dipolar correlation experiment to examine the 31P line width, which is reduced by motion at higher temperatures. It was shown that the line width of the P2S7 unit is attributable to the distribution of local structures of and around the P2S7 ditetrahedra unit. With these, we concluded that the significant motional fluctuation of the P2S7 ditetrahedra unit at above 310 K allows facile diffusive motion of lithium ions, leading to the high ionic conductivity.

Rechargeable lithium-ion batteries (LIBs) are currently accepted to be one of the most suitable energy storage resources in portable electronic devices because of their high gravimetric and volumetric energy density. To understand the behavior of Li + ions on electrochemical lithium extraction/insertion process, we performed in situ 7 Li nuclear magnetic resonance (NMR) measurements for LiCoO 2 cathode in a plastic cell battery, and the spectral evolutions of the 7 Li NMR signal of Li x CoO 2 (0 ≤ x ≤ 1) were well investigated. Very narrow solid solution region of Li x CoO 2 (∼0.99 ≤ x < 1) was explicitly defined from the large intensity reduction of LiCoO 2 signal at ∼0 ppm, which is related to the localized nature of the electronic spin of paramagnetic Co 4+ ion formed at the very early delithiation stage. With further decreasing the signal intensity of LiCoO 2 , a Knight-shifted signal corresponding to an electrically conductive Li x CoO 2 phase emerged at x = 0.97, which then monotonously decreased in intensity for x < 0.75 in accordance with the electrochemical lithium de-intercalation from Li x CoO 2. These observations acquired in situ fully confirm the earlier studies obtained in ex situ measurements, although the present study offers more quantitative information. Moreover, it was shown that the peak position of the NMR shift for Li x CoO 2 moved as a function of lithium content, which behavior is analogous to the change in its c lattice parameter. Also, the growth and consumption of dendritic/mossy metallic lithium on the counter electrode was clearly observed during the charge/discharge cycles.

Delithiation and lithiation behaviors of ordered spinel LiNi 0.5 Mn 1.5 O 4 and disordered spinel LiNi 0.4 Mn 1.6 O 4 were investigated by using in situ (in operando) 7 Li NMR and ex situ 6 Li MAS NMR spectroscopy. The in situ 7 Li monitoring of the ordered spinel revealed a clear appearance and subsequent disappearance of a new signal from the welldefined phase Li 0.5 Ni 0.5 Mn 1.5 O 4 , suggesting the two-phase reaction processes among Li 1.0 Ni 0.5 Mn 1.5 O 4 , Li 0.5 Ni 0.5 Mn 1.5 O 4 , and Li 0.0 Ni 0.5 Mn 1.5 O 4 . Also, for the disordered spinel, Li 0.5 Ni 0.4 Mn 1.6 O 4 was identified with a broad distribution in Li environment. High-resolution 6 Li MAS NMR spectra were also acquired for the delithiated and lithiated samples to understand the detailed local structure around Li ions. We suggested that the nominal Li-free phase Li 0.0 Ni 0.5 Mn 1.5 O 4 can accommodate a small amount of Li ions in its structure. The tetragonal phases Li 2.0 Ni 0.5 Mn 1.5 O 4 and Li 2.0 Ni 0.4 Mn 1.6 O 4 , which occurred when the cell was discharged down to 2.0 V, were very different in the Li environment from each other. It is found that 6,7 Li NMR is highly sensitive not only to the Ni/Mn ordering in LiNi 0.5 Mn 1.5 O 4 but also to the valence changes of Ni and Mn on charge−discharge process.