Effects of Ca substitution on the local structure and oxide–ion behavior of layered perovskite lanthanum nickelate

La2NiO4+δ-based materials with a layered perovskite structure have attracted significant attention as air–electrode materials for use in solid oxide fuel cells. In particular, Ca-substituted materials, La2-xCaxNiO4+δ, have been investigated, as the partial substitution of La with Ca can improve oxide–ion conduction in crystals. However, the local structures around the conducting oxide ion and Ca dopant are not been well understood because their distributions cannot be characterized by a general structure analysis only using Bragg peaks. Therefore, we examine the atomic structure of La1.75Ca0.25NiO4+δ by a combination of molecular dynamics simulations and a reverse Monte Carlo modeling using the Faber–Ziman structure factor, real-space function, and the Bragg profile simultaneously. The results indicate that conducting oxide ions are introduced into rocksalt layers in the crystal and are present around La but not Ca. Furthermore, it is found that ionic diffusion is accompanied by a change in the rocksalt layer volume, which can be suppressed by the partial substitution with Ca. This can be regarded as a major reason why Ca substitution improves oxide–ion diffusion in the La2NiO4+δ layered perovskite

Safety Test Methods Simulating Internal Short Circuit and the Mechanism for Safety Improvement of Li-ion Batteries by Heat Resistant Separators

It is widely recognized that heat-resistant separators improve the safety of lithium-ion batteries. However, it is not clear how the separator contributes to battery safety, or how much heat resistance is required. The state of separators when a short circuit occurs in batteries was simulated and the following tests were conducted. As a first test, the edges of the separator were restrained, and hot air was applied only to a limited part of the specimen. For the second test, a model battery system was constructed and electrical heat generation during the early stage of a short circuit was observed. In these tests, several types of separators were compared with respect to the extent of damage and electrical heat generation. The separators that gave good results during nail penetration tests showed limited damage and electrical heat generation during the previously discussed tests. The heat resistance of a separator should be discussed with regard to whether it can maintain the separator function during electrical heat generation via short circuit

Theoretical Study Using First-Principles Calculations of the Electronic Structures of Magnesium Secondary Battery Cathode Materials MgCo2−xMnxO4 (x = 0, 0.5) in the Pristine and Discharged States

In this study, the projected density of states (PDOS) of the stable normal-spinel structure and stable Mg/Co mixed-cation spinel structure of Mg1+yCo2−xMnxO4 (x = 0, 0.5; y = 0, 0.5, 1) in the pristine and discharged states are obtained using first-principles calculations. The spin state and the valence state of the transition metals are investigated. The overlaps of the d orbitals of the transition metals and the p orbitals of oxygen are large, and the covalency between the transition metal and oxygen is strong in the pristine MgCo2O4 and MgCo1.5Mn0.5O4. The M–O6 (M = Co, Mn) octahedra become stable as a host structure. From the PDOS spectra, Co atoms are in the trivalent low-spin state in pristine MgCo2O4 and MgCo1.5Mn0.5O4 and Mn atoms are nearly tetravalent in pristine MgCo1.5Mn0.5O4. In the discharge process, the overlap of the d orbitals of the transition metals and the p orbitals of oxygen becomes narrow and the valence of the transition metals decreases with increasing Mg insertion. The results of the first-principles calculations are consistent with those of X-ray absorption near edge structure spectra

Effect of Separator and Anode on Electrochemical Characteristics and Crystal Structure of Lithium-ion Battery Cathode Material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2

We studied the average crystal structural change during charging and discharging of a 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 battery cathode in combination with a Li-metal anode, graphite anodes, and three types of separators. Prelithiation of the graphite anode enabled stable charge and discharge of the cathode. The average structure of the cathode after the 5th discharge did not change significantly due to the difference in the anodes and separators. However, after the 55th discharge, the difference in the electron density distribution and the distortion of the M-O6 octahedra for the different separators increased. The findings suggest that the changes in the crystal structure of a cathode over a long-term cycle should be studied with the anodes and separators used in actual batteries rather than Li-metal anodes and conventional separators

Electrochemical Properties and Crystal and Electronic Structures of Spinel αMgCo2−xMnxO4-(1 − α)Mg(Mg0.33V1.67−yNiy)O4 for Magnesium Secondary Batteries

In the present study, αMgCo1.5Mn0.5O4-(1 − α)Mg1.33V1.57Ni0.1O4 was synthesized by a reverse co-precipitation method. The products were assigned to a spinel structure with a space group Fd3m based on powder X-ray diffraction analysis. Inductively coupled plasma-atomic emission spectroscopy revealed that the composition was not close to the target composition; the Mg content was higher and the V content was lower than expected. Charge/discharge cyclic tests showed that the discharge capacity exceeded 180 mAh g−1 and that the cyclability was reversible up to 60 cycles at 90 °C with a cut-off voltage of 0.945 to −1.055 V vs. Ag/Ag+ (3.545–1.545 V vs. Mg/Mg2+) for α = 0.3. The electronic structure was analyzed using the maximum-entropy method based on a Rietveld analysis, and it was found that Mg insertion was easier for α = 0.3, 0.5, 0.9 than for MgCo1.5Mn0.5O4 and Mg1.33V1.57Ni0.1O4. The strain in MO6 octahedra for α = 0.1, 0.3, 0.5, 0.7 was smaller than that for MgCo1.5Mn0.5O4 and Mg1.33V1.57Ni0.1O4, which suggests that the host structure was stabilized by forming a solid solution. A Rietveld analysis after the first discharge and second charge confirmed a partly reversible phase transition from the spinel phase to a rock-salt phase. The valence of the transition metals was examined by X-ray absorption fine structure (XAFS) measurements, and the Co and Mn K-edge spectra revealed that Co and Mn were present as Co2.67+ to Co2+ and Mn4+ to Mn3+ species for α = 0.3. Both Co and Mn redox processes are considered to contribute to Mg intercalation. Extended XAFS (EXAFS) Co K-edge and Mn K-edge spectra for the powder specimens and after the first discharge and second charge showed that bonds between Co, V atoms and nearest-neighbor O atoms were distorted after the first discharge, and that this distortion was relaxed after the second charge