Hydrogen-bonding-mediated structural stability and electrochemical performance of iron fluoride cathode materials

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 3; no. 31; pp. 16222 - 16228
• Main Authors: Li, Zuosheng, Wang, Beizhou, Li, Chilin, Liu, Jianjun, Zhang, Wenqing
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Cathodes; Distortion; Electrochemical analysis; Hydrogen bonding; Iron; Stability; Strength; Transportation
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta03327f

Numerous lithium ion battery cathode materials containing trace amounts of water accommodated in Li + transportation tunnels have been experimentally synthesized. However, the impact of water on structural stability and electrochemical performance of cathode materials is still unclear. Here, the first-principles calculations combining thermodynamic analysis of Li x FeF 3 ·0.33H 2 O were performed to unravel the interaction mechanism among frameworks of FeF 3 , H 2 O, and Li + . The FeF 3 framework structure distortion is mitigated by hydrogen bonding between isolated H 2 O and F − ions, bringing opposite effects on the stability of hydrogen bonding and instability of structural distortion. The hydrogen bonding strength of F − H 2 O can be further mediated by the Li + -inserted amount, which indirectly results in a wide discharge voltage window of 2.2 to 3.6 V. The Li + transportation barrier in cooperative mode is also tuned by the flexible hydrogen bonding strength due to different occupied positions. Li 0.66 FeF 3 ·0.33H 2 O is determined as the most stable species and more Li + insertion directly leads to the conversion reaction FeF 6 3− → FeF 4 − + 2F − . Therefore, stabilizing Fe-F bonds and reducing octahedral chain distortion are important to improve the electrochemical performance of FeF 3 cathode materials with water. Tunable H 2 O-F − hydrogen bonding is crucial to the structural stability and electrochemical performance of FeF 3 ·0.33H 2 O cathode materials.