Reversible Structural Changes and High-Rate Capability of Li3PO4‑Modified Li2RuO3 for Lithium-Rich Layered Rocksalt Oxide Cathodes

• Published in: Journal of physical chemistry. C Vol. 122; no. 29; pp. 16607 - 16612
• Main Authors: Taminato, Sou, Hirayama, Masaaki, Suzuki, Kota, Kim, KyungSu, Tamura, Kazuhisa, Kanno, Ryoji
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.07.2018
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b04723

Lithium-rich layered rocksalt oxides are promising cathode materials for lithium-ion batteries, owing to their high charge–discharge capacities of over 250 mA h g–1. However, their poor rate capability remains to be addressed. Here, we investigate the effects of surface modification by amorphous Li3PO4 on the structures and electrochemical reactions in the surface region of an epitaxial Li2RuO3(010) film electrode fabricated by pulsed laser deposition. Structural characterization using surface X-ray diffraction (XRD), hard X-ray photoemission spectroscopy, and neutron reflectometry shows that surface modification by 3 nm thick Li3PO4 resulted in the partial substitution of P for Li in the surface region of Li2RuO3. The modified (010) surface exhibits better rate capability at 20 C (41% of the discharge capacity at 0.3 C) compared to the unmodified surface (5% of that at 0.3 C). In situ surface XRD confirmed that highly reversible structural changes occurred at the modified surface during lithium (de)­intercalation, whereas the unmodified surface showed irreversible structural changes. These results demonstrate that this surface modification stabilizes the crystal structure in the surface region, and it can improve the rate capability of lithium-rich layered rocksalt oxide cathodes.