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

Yanagita, Ayumu  ,  Shibata, Takayuki  ,  Kobayashi, Wataru  ,  Moritomo, Yutaka

3 ( 10 )  , p.106104 , 2015-10 , AIP Publishing
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.

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