First-principles study on the stability, electrochemical property, and degradation mechanism of ceramic electrode materials
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First-principles studies demonstrate the capability to rapidly and accurately calculate desired properties in battery materials. This thesis focuses on the examination of layered NaCrO2 as a case study to assess the impact of various calculation methods. Additionally, a microscopic analysis is... Show moreFirst-principles studies demonstrate the capability to rapidly and accurately calculate desired properties in battery materials. This thesis focuses on the examination of layered NaCrO2 as a case study to assess the impact of various calculation methods. Additionally, a microscopic analysis is conducted to investigate the failure mode of NaCrO2. Lastly, a successful first-principles based high-throughput screening of electrode materials is performed to identify stable compounds that enable easy Li migration.The layered O3 NaCrO2 compound exhibits promising characteristics as a Na-ion cathode material, including good thermal stability and specific capacity. However, it suffers from poor rate capability. To address this limitation and develop high-rate Na-ion cathodes, we conducted a first-principles study that focused on the stability and Na diffusion in pure and doped NaCrO2. The study utilized various functionals, including those explicitly incorporating van der Waals (vdW) interactions. By including vdW interactions, we observed a significant reduction in interlayer distances within partially desodiated NaCrO2, which directly impacted the prediction of Na diffusion barriers. We established a linear relationship between interlayer distance and diffusion barrier using different functionals. Notably, the increased diffusion barriers were mainly due to the reduced interlayer distances predicted by the vdW-inclusive functionals, rather than the inclusion of vdW interactions in the transition state calculations. Other factors, such as the charge density change introduced by different dopants, also influenced the Na diffusion barriers. Metal doping (Al, Zn, Mn, and Co) at low concentrations in NaCrO2 had minor effects on its thermodynamic stability but significantly promoted Na diffusivity. Among the doped NaCrO2 compounds, Co-doped NaCrO2 exhibited the lowest Na diffusion barriers and emerged as a potential candidate for high-rate Na-ion cathode materials. This study highlights the significance of vdW interactions in layered transition metal oxides and provides strategies to enhance first-principles predictions for such structures.Then, TM migration usually occurs at highly charged states in layered Na transition metal oxide, leading to a deterioration in capacity and reversibility. Furthermore, the formation of hybrid phases, characterized by the intergrowth of octahedral and prismatic Na layers, is known to take place at highly charged states. These hybrid phases often exhibit greater stability compared to simple O3 or P3 stacking configurations. However, there is limited understanding regarding the mechanism and impact of TM migration in these hybrid phases. To address this gap, we conducted a comparative first-principles study to elucidate the connection between structural changes and Cr migration in layered O3 and hybrid-phased NaCrO2. We observed that the hybrid-phased NaCrO2 experienced more significant layer shrinkage than the O3 phase after Cr migration. Three factors were found to affect the Cr migration energy: the Na concentration, local 3D configuration, and 2D in-plane geometry. Low Na concentration and specific 3D configurations facilitated Cr migration. Furthermore, the Cr migration barriers in both O3 and hybrid-phased NaCrO2 were found to be positively correlated with Cr migration energy. Lastly, we surveyed the Cr migration of 17 doped O3 and hybrid-phased NaCrO2 compounds. A uniform distribution of Cr-O bond length usually indicated suppressed Cr migration. We identified optimal dopants for Cr migration suppression by considering both Cr and dopant migration energy. This comparative study on Cr migration in O3 and hybrid-phased NaCrO2 highlights the significant role of hybrid phases in the application of layered cathode materials.Moving from the calculations of single material system, we last conduct a first-principles high-throughput screening of multicomponent transition metal sulfides (TMS) as fast Li-ion intercalation compounds. We compared two representative TMS frameworks, pyrite and spinel, with regard to their selectivity in forming stable disordered TMS. To quantify the ability to form entropy stabilized disordered TMS, we examined the effects of cation permutation on the formation enthalpy range. Although low energy-above-hull (Ehull) is a preliminary requirement for the formation of stable TMS, a narrow formation enthalpy range can also lead to entropy stabilized TMS, as only a small amount of excess energy is required to stabilize the metastable configurations. Among the 70 pyrite and spinel frameworks studied, we selected 13 spinel compounds based on their low Ehull and narrow Ef range. Additionally, these spinel compounds exhibited greater stability compared to their pyrite counterparts. We found that early transition metal elements such as Ti and V were less favorable for the formation of pyrite TMS, while late TM elements, especially Cu, strongly destabilized spinel TMS. The spinel (CrMnCoNi)S2 TMS demonstrated the most promising characteristics with a narrow Ef range. Finally, we calculated and ranked the Li migration barriers in the 13 stable spinel TMS using a bond valence-based method, which allowed for quick screening of ion migration. High oxidation state TM elements, such as Mn4+ and Cr3+, located nearest to the Li migration path, increased the Li migration barrier. (CrMnCoNi)S2 exhibited the lowest Li migration barrier, positioning it as a promising entropy-stabilized spinel intercalation compound. Show less
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