Scaling relation between renormalized discharge rate and capacity in Na x CoO2 films

• Published in: APL Materials Vol. 3; no. 10; p. 106104
• Main Authors: 小林 航, 守友 浩, Yanagita Ayumu, Shibata Takayuki, Kobayashi Wataru, Moritomo Yutaka
• Format: Journal Article
• Language: English
• Published: AIP Publishing 01.10.2015
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.4933236

Layered cobalt oxide, P2-Na x CoO2, is a prototypical cathode material for sodium-ion secondary battery. We systematically investigated the rate dependence of the discharge capacity (Q) in three thin films of Na 0.68CoO2 with different film thickness (d) and in-plane grain radius (r). With subtracting conventional voltage drop effect on Q, we derived an intrinsic rate dependence of Q. We found a scaling relation between the renormalized discharge rate (γ ≡ r 2/DT; D and T are the Na + diffusion constant and discharge time, respectively) and relative capacity (=Q/Q 0; Q 0 is the value at a low rate limit). The observed scaling relation is interpreted in terms of the Na + intercalation process at the electrolyte-Na x CoO2 interface and Na + diffusion process within Na x CoO2.