Enhanced Lithium Diffusivity in Reduced Cerium Oxides: A First-Principles Study

Abstract

Cerium oxide is considered as a promising protective coating material for the high-energy cathode of a Li-ion battery (LIB) against surface structural degradation. However, detailed knowledge on how Li migrates in cerium oxide is still limited, which is important for further development of cerium oxide as an LIB high-energy cathode coating material. Herein, using first-principles density functional theory calculations, we investigate Li insertion and diffusion mechanisms in pristine CeO2, reduced CeO2 with oxygen vacancy, and Ce2O3 as a representative material for highly reduced cerium oxide. For two different concentrations (1:8 and 1:27 Li:Ce), we find that Li can occupy empty octahedral sites of CeO2 in either the neutral or ionized state. Li diffusion in fluorite CeO2 is isotropic to the ⟨110⟩ direction, and the energetic barrier is significantly high. An addition of O vacancy in the CeO2 fluorite structure breaks the isotropy of Li diffusion; the barrier is decreased if the vacancy is located unidirectional with the ⟨110⟩ direction, and the barrier is increased if it is in the opposite of the ⟨110⟩ direction. In the highly reduced CeO2, i.e., Ce2O3, we observe that Li can only intercalate in the ionized Li+ state. The diffusion barrier of Li+ in this structure is significantly lower compared to the previous pristine and reduced CeO2 in two different concentrations, i.e., 1:2 and 1:16 Li:Ce. This indicates that the degree of reduction highly correlates to Li diffusivity in cerium oxide. Therefore, applying a highly reduced and O-poor CeO2 coating is suggested to allow fast and nonobstructive Li diffusion.

Enhancing the Electrochemical Properties of Nickel-Rich Cathode by Surface Coating with Defect-Rich Strontium Titanate

“…In comparison, NCA-STOx demonstrates a marginally higher discharge capacity of ∼218 mA h/g and a better initial Coulombic efficiency of 87.7%. The slight enhancement of initial specific capacity could originate (1) from the thin STOx coating layer not dramatically affecting the Li insertion process into the Ni-rich cathode materials, (2) the OVs in the STOx coating layer acting as a Li + diffusion pathway that plays a positive role in the Li + migration at the interface between NCA and STOx, which has been proposed by Komalig et al recently, 29 and (3) the higher electrical conductivity introduced by STOx. Generally, Ni-rich oxide materials show relatively poor electrical conductivity and require conductive agents (such as carbon black) during cathode preparation to increase the conductivity of the whole system.…”

Unveiling the role of lithium in cerium oxide based ceramic fuel cells employing lithium compounds as the anode

“…The dopant of lithium is an electron donor resource, which further reduces the Ce 4+ to Ce 3+ except for the hydrogen reduction. 30 Moreover, the Li + is clearly detected in the nitrogen side for type B cells after hydrogen treatment, whereas no peak for Li 1s is found for the type A cell after treatment (Fig. 1f).…”

Storage Performance and Structure Degradation Mechanism of Single-Crystal Ni-Rich Material

“…The high potential difference during the first charge/discharge is caused by the removal of residual lithium compounds on the stored SCNCM surface. 49,50 The results indicate that many impurities appear on the SCNCM surface after long-time storage, affecting the transfer of Li ions. In the charge/ discharge curves, the SCNCM materials stored for 7 days have an apparent overvoltage peak at the beginning of charging.…”