KVOPO4: A New High Capacity Multielectron Na‐Ion Battery Cathode

• Published in: Advanced energy materials 2018-07, Vol.8 (21), p.n/a
• Main Authors: Ding, Jia, Lin, Yuh‐Chieh, Liu, Jue, Rana, Jatinkumar, Zhang, Hanlei, Zhou, Hui, Chu, Iek‐Heng, Wiaderek, Kamila M., Omenya, Fredrick, Chernova, Natasha A., Chapman, Karena W., Piper, Louis F. J., Ong, Shyue Ping, Whittingham, M. Stanley
• Format: Article
• Language: English
• Subjects: Cathodes; Conductors; Density functional theory; Electrode materials; energy storage (including batteries and capacitors), defects, charge transport, materials and chemistry by design, synthesis (novel materials); Flux density; high capacity; high energy; Lithium; Lithium-ion batteries; Migration; multielectron; Rechargeable batteries; Sodium; Sodium-ion batteries; vanadyl phosphate
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201800221

Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi‐electron cathode material, KVOPO4, for sodium ion batteries. Due to the unique polyhedral framework, the V3+ ↔ V4+ ↔ V5+ redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO4 based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na+ per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg−1. Combining an average voltage of 2.56 V vs. Na/Na+, a high practical energy density of over 600 Wh kg−1 was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO4 framework is a 3D ionic conductor with a reasonably, low Na+ migration energy barrier of ≈450 meV, in line with the good rate capability obtained. KyVOPO4, is a new intercalation host for sodium batteries. The V3+ ↔ V4+ ↔ V5+ redox couple is for the first time fully activated by sodium ions in a vanadyl phosphate phase, delivering a high specific capacity of 235 Ah kg−1, and an energy density of over 600 Wh kg−1.