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The charging speed of lithium-ion batteries can be enhanced by improving the diffusion performance of Li ions inside and at the interface of their cathodes. In this study, we applied strain to LiCoO2(LCO) cathode materials to elongate their lattices, and the relationship between the lattice strain and energy required for Li deintercalation, referred to as “Li vacancy formation energy,” was estimated by ab-initiocalculations to determine the optimal strain. The results suggest that the charging speed can be improved by adding a strain of less than 5% while retaining its high mechanical properties and equilibrium potential. Furthermore, we found that applying approximately 10% strain in the c-axis direction significantly reduces the Li vacancy formation energy of the LCO cathode.We applied strain to LiCoO2cathodes to elongate their lattices, and the relationship between the lattice strain and energy required for Li deintercalation was estimated by ab-initiocalculations. We found that the charging speed can be improved by adding a strain of less than 5% while retaining its high mechanical properties and equilibrium potential.

We investigated and compared various mechanical properties of two major cathode materials (LiCoO2(LCO) and LiNi0.33Co0.33Mn0.33O2(NCM)), which are particularly susceptible to degradation among components of lithium-ion batteries. In this analysis, ab initiocalculations using density functional theory (DFT) are adopted. The plotting of stress-strain curves and mechanical characterization of Li-deintercalated structures are conducted in addition to conventional elastic tensor calculations. In this study, the elastic moduli (stiffness) of LCO and NCM are similar, however, the strength and durability of the NCM cathode in the c-axis direction are clearly lower than those of LCO. These approaches can be applied to the mechanical characterization of new promising cathodes in the future.We conducted various mechanical chcaracterization of two major cathode materials: LiCoO2(LCO) and LiNi0.33Co0.33Mn0.33O2(NCM) using ab-initiocalculations, including the plotting of stress-strain curves and mechanical characterization of Li-deintercalated structures. Our main results are that the stiffness of LCO and NCM are similar whereas the strength and durability of the NCM cathode are clearly lower than those of LCO.

In the application of density functional theory (DFT) calculations to LiCoO2(LCO) cathode material of lithium-ion batteries, this study investigates the differences between the obtained values for lattice constants, elastic constants, and stress-strain curves using different calculation condition such as exchange-correlation energy functionals; additionally, it attempts to improve the accuracy of the mechanical characterization of the DFT calculation. The results reveal that the adoption of Perdew-Wang (PW91) functional with dispersion corrections is better in the structural optimization of the DFT calculation for the LCO cathode compared with other calculation conditions, such as the adoption of Perdew-Burke-Ernzerhof (PBE) and revised PBE for solids (PBE-solid), which have been used in previous studies. The high accuracy of the lattice constant calculations in the structural optimization using PW91 results in a relatively high evaluation accuracy of the mechanical properties of these cathode materials. Additionally, a strong correlation between the lattice (or lattice volumes) and elastic constants is observed; evidently, a slight deviation in the lattice constants causes a relatively significant change in the elastic constants. In some of the calculation results for stress-strain curves, differences in the elastic limits (elastic regions) dependent on the selected exchange-correlation functionals are clearly observed.In the ab-initiocalculations using density functional theory, we estimate the mechanical properties of LiCoO2(LCO) cathode material and seek better exchange-correlation functionals. Our study reveals that the Perdew-Wang (PW91) functional is better in the structural optimization and estimation of mechanical properties of LCO compared with other functionals.

AbstractIn Korea, mass mortality of Quercus mongolicatrees has become obvious since 2004. Raffaelea quercus-mongolicaeis believed to be a causal fungus contributing the mortality. To evaluate the pathogenicity of the fungus to the trees, the fungus was multiple- and single-inoculated to the seedlings and twigs of the mature trees, respectively. In both the inoculations, the fungus was reisolated from more than 50% of inoculated twigs and seedlings. In the single inoculations, proportions of the transverse area of non-conductive sapwood at inoculation points and vertical lengths of discoloration expanded from the points were significantly different between the inoculation treatment and the control. In the multiple inoculations, no mortality was confirmed among the seedlings examined. These results showed that R. quercus-mongolicaecan colonize sapwood, contribute to sapwood discoloration and disrupt sap flows around inoculation sites of Q. mongolica, although the pathogenicity of the fungus was not proven.