Browsing by Author "Liu, B"
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- ItemAb initio thermodynamic optimization of Ni-rich Ni–Co–Mn oxide cathode coatings(Elsevier, 2020-02-29) Liu, B; Liu, JH; Yang, J; Wang, D; Ye, CC; Wang, DY; Avdeev, M; Shi, S; Yang, JH; Zhang, WQThe effectiveness of surface coatings in improving the stability and cycling performance of cathodes has been demonstrated since they are first proposed in the 1990's. However, the progress since then is made mostly using the trial-and-error method. Herein, an automated electrochemical-chemical stability design scheme based on first-principles thermodynamics calculations of reaction models is presented to optimize coatings for Ni-rich nickel–cobalt–manganese oxide (NCM) cathodes. Given that the coating must possess a wider electrochemical window than the cathode without the occurrence of Li-ion redistribution at the cathode/coating interface, the reaction energies of both lithium insertion/extraction and decomposition process associated with the coating are used as one of the two screening criteria. As the coating is also required to be chemically stable in Li residues and hydrofluoric-acid containing liquid environment, the positive reaction energy achieved by adjusting molar ratio of the components is used as another criterion. Using these two screening criteria, we demonstrate that lithium-containing metal phosphates, rather than previously suggested Li-containing metal oxides, are the optimal coatings for Ni-rich NCM cathodes, which is confirmed experimentally. The proposed approach is general and can be used to find optimal coating materials for any other cathodes. © 2020 Elsevier B.V.
- ItemHigh-throughput computational screening of Li-containing fluorides for battery cathode coatings(American Chemical Society, 2020-12-16) Liu, B; Wang, D; Avdeev, M; Shi, S; Yang, J; Zhang, WQCathode degradation is a key factor that limits the cycling stability and rate capability of Li-ion batteries. Coating the surface of cathode particles with metal oxides or fluorides has been reported to suppress this degradation. However, poor Li-ion conductivity of metal oxide and fluoride coatings typically decreases the overall ionic conductivity. In addition, side (electro)chemical reactions at the coating/cathode interface and coating/hydrofluoric acid liquid environment also limit the performance of Li-ion batteries. Identification of stable coating materials with high Li-ion conductivity, which is typically done via a trial-and-error approach, remains a challenge. In this work, we perform high-throughput computational screening of ternary Li-containing fluorides for application as cathode coatings for Li-ion batteries, focusing on their phase stability, electrochemical stability, chemical stability, and Li-ion conductivity. Using the tiered screening approach, we identify 10 promising coating candidates from all the 920 Li-containing fluorides listed in the Materials Project database, including the two experimentally studied Li2ZrF6 and Li2TiF6 compounds. The identified cathode coatings are expected to exhibit optimal battery cycling and rate performance. In particular, Li2MF6 (M = Si, Ge, Zr, Ti) compounds offer the best combination of electrochemical and chemical stability and ionic conductivity, surpassing the performance of common coatings such as oxides and binary fluorides. © 2019 American Chemical Society