Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO ₄ over Multiple Lithium Intercalation

Journal Article · Tue Mar 22 00:00:00 EDT 2016 · Chemistry of Materials

DOI:https://doi.org/10.1021/acs.chemmater.5b04880· OSTI ID:1391749

Lin, Yuh-Chieh; Wen, Bohua; Wiaderek, Kamila M.; Sallis, Shawn; Liu, Hao; Lapidus, Saul H.; Borkiewicz, Olaf J.; Quackenbush, Nicholas F.; Chernova, Natasha A.; Karki, Khim; Omenya, Fredrick; Chupas, Peter J.; Piper, Louis F. J.; Whittingham, M. Stanley; Chapman, Karena W.; Ong, Shyue Ping

ε -Li x VOPO 4 is a promising multi-electron cathode for rechargeable lithium-ion bat- teries that has an extremely high theoretical capacity of 318 mAh/g. In this w ork, we demonstrate the stable cycling of more than one Li in solid-state-syn thesized ε - LiVOPO 4 over more than 20 cycles for the first time. Using a combination of densit y functional theory (DFT) calculations, X-ray pair distribution funct ion (PDF) analy- sis and X-ray Absorption Near Edge Structure (XANES) measurements, we pre sent a comprehensive analysis of the thermodynamics, kinetics and stru ctural evolution of ε -Li x VOPO 4 over the entire lithiation range. We identify two intermediate ph ases at x = 1 . 5 and 1.75 in the low-voltage regime using DFT calculations, and the comput ed and electrochemically measured voltage profiles are in excellent agree ment. Operando PDF techniques show a reversible hysteretic change in the short ( < 2° A) V-O bond lengths coupled with an irreversible extension of the long V-O bond ( > 2.4 °A) dur- ing low-voltage cycling. These observations are confirmed with EXAFS spe ctra. We identify hydrogen intercalation from the electrolyte decomposition as a likely explana- tion for the ~ 2 . 4°A V-O bond and its irreversible extension. In terms of electronic conductivity, we find Li x VOPO 4 to be a large band gap insulator across the entire lithiation range, and calculated small polaron migration barriers are similar to those of the olivine LiMPO 4 cathodes. Finally, we demonstrate that ε -LiVOPO 4 is likely to be a one-dimensional diffuser using climbing-image nudged elastic ban d calculations. These results highlight the importance of nano-sizing and carbon coating in achieving good electrochemical performance in this material.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1391749
• Journal Information: Chemistry of Materials, Vol. 28, Issue 6; ISSN 0897-4756
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English