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Fast discharge process of layered cobalt oxides due to high Na⁺ diffusion.

Shibata T, Fukuzumi Y, Kobayashi W, Moritomo Y - Sci Rep (2015)

Bottom Line: We found that the D values (~ 0.5-1.5 × 10(-10) cm(2)/s) of Na(+) are higher than those (< 1 × 10(-11) cm(2)/s) of Li(+) in layered LiCoO2.We further found that the activation energy (ED ~ 0.4 eV) for the Na(+) diffusion is significantly low in these layered cobalt oxides.We found a close relation between the relative capacity and the renormalized discharge rate ( = L(2)/DT, where L and T are the film thickness and discharge time, respectively).

View Article: PubMed Central - PubMed

Affiliation: Fucalty of Pure and Applied Science, Univ. of Tsukuba, Tsukuba 305-8571, Japan.

ABSTRACT
Sodium ion secondary battery (SIB) is a low-cost and ubiquitous secondary battery for next-generation large-scale energy storage. The diffusion process of large Na(+) (ionic radius is 1.12 Å), however, is considered to be slower than that of small Li(+) (0.76 Å). This would be a serious disadvantage of SIB as compared with the Lithium ion secondary battery (LIB). By means of the electrochemical impedance spectroscopy (EIS), we determined the diffusion constant (D) of Na(+) in thin films of O3- and P2-type NaCoO2 with layered structures. We found that the D values (~ 0.5-1.5 × 10(-10) cm(2)/s) of Na(+) are higher than those (< 1 × 10(-11) cm(2)/s) of Li(+) in layered LiCoO2. Especially, the D values of O3-NaCoO2 are even higher than those of P2-NaCoO2, probably because O3-NaCoO2 shows successive structural phase transitions from the O3, O'3, P'3, to P3 phases with Na(+) deintercalation. We further found that the activation energy (ED ~ 0.4 eV) for the Na(+) diffusion is significantly low in these layered cobalt oxides. We found a close relation between the relative capacity and the renormalized discharge rate ( = L(2)/DT, where L and T are the film thickness and discharge time, respectively).

No MeSH data available.


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Discharge curves of films of (a) O3-NaCoO2 and (b) P2-NaCoO2.Film thicknesses (L) are 320 nm and 330 nm, respectively.
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f3: Discharge curves of films of (a) O3-NaCoO2 and (b) P2-NaCoO2.Film thicknesses (L) are 320 nm and 330 nm, respectively.

Mentions: The open-current-voltage (OCV) discharge curve slightly different between O3-type and P2-type NaCoO2 (black curves in Fig.3). The layered cobalt oxides are known to show successive structural phase transition with Na+ intercalation/deintercalation. The phase transition causes the voltage drop at single phase point and the voltage plateau in two phase region. Lie. et al.21 systematically investigated the structural properties of O3-NaxCoO2 against x. They found four phases, i.e., the O3 (x = 1.00), O’3 (monoclinic phase: x = 0.83), P’3 (monoclinic phase: x = 0.67), and P3 (x ~0.5) phases. In the O’3phase, Na+ is located in the oxygen octahedron as in the O3-type. In the P’3 and P3 phases, Na+ is located in the oxygen prisms as in the P2-type. Actually, we observed four voltage drops in the discharge curve of O3-NaCoO2, which correspond to the O3, O’3, P’3 and P3 phases (Fig. S8). In addition, the inter CoO2-sheet distance (~ 5.44 Å) of the oxidized film (x = 0.65) is much longer than that (~ 5.14 Å) of the as-grown film, (Fig. S3) suggesting the P3-type structure21. These observations indicate that the O3-NaxCoO2 film (0.5 < x < 0.83) contains the P3 (or P’3) phases. Then, the unexpected high-D values observed in O3-NaCoO2 [see Fig.3(c)] are ascribed to the P3-type host framework with oxygen prisms. On the other hand, Berthelot et al.8 investigated the structural properties of P2-NaxCoO2 against x. They found three phases, i.e., the x = 0.72, 0.76, and 0.79 phases, in addition to the well-known x = 1/2 and 2/3 phases. These phases are ascribed to the Na+/vacancy ordering within the P2-type host framework. We observed three voltage drops in the discharge curve of P2-NaCoO2, which correspond to the 1/2, 3/2, and ~ 0.76 phases (Fig. S8).


Fast discharge process of layered cobalt oxides due to high Na⁺ diffusion.

Shibata T, Fukuzumi Y, Kobayashi W, Moritomo Y - Sci Rep (2015)

Discharge curves of films of (a) O3-NaCoO2 and (b) P2-NaCoO2.Film thicknesses (L) are 320 nm and 330 nm, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355731&req=5

f3: Discharge curves of films of (a) O3-NaCoO2 and (b) P2-NaCoO2.Film thicknesses (L) are 320 nm and 330 nm, respectively.
Mentions: The open-current-voltage (OCV) discharge curve slightly different between O3-type and P2-type NaCoO2 (black curves in Fig.3). The layered cobalt oxides are known to show successive structural phase transition with Na+ intercalation/deintercalation. The phase transition causes the voltage drop at single phase point and the voltage plateau in two phase region. Lie. et al.21 systematically investigated the structural properties of O3-NaxCoO2 against x. They found four phases, i.e., the O3 (x = 1.00), O’3 (monoclinic phase: x = 0.83), P’3 (monoclinic phase: x = 0.67), and P3 (x ~0.5) phases. In the O’3phase, Na+ is located in the oxygen octahedron as in the O3-type. In the P’3 and P3 phases, Na+ is located in the oxygen prisms as in the P2-type. Actually, we observed four voltage drops in the discharge curve of O3-NaCoO2, which correspond to the O3, O’3, P’3 and P3 phases (Fig. S8). In addition, the inter CoO2-sheet distance (~ 5.44 Å) of the oxidized film (x = 0.65) is much longer than that (~ 5.14 Å) of the as-grown film, (Fig. S3) suggesting the P3-type structure21. These observations indicate that the O3-NaxCoO2 film (0.5 < x < 0.83) contains the P3 (or P’3) phases. Then, the unexpected high-D values observed in O3-NaCoO2 [see Fig.3(c)] are ascribed to the P3-type host framework with oxygen prisms. On the other hand, Berthelot et al.8 investigated the structural properties of P2-NaxCoO2 against x. They found three phases, i.e., the x = 0.72, 0.76, and 0.79 phases, in addition to the well-known x = 1/2 and 2/3 phases. These phases are ascribed to the Na+/vacancy ordering within the P2-type host framework. We observed three voltage drops in the discharge curve of P2-NaCoO2, which correspond to the 1/2, 3/2, and ~ 0.76 phases (Fig. S8).

Bottom Line: We found that the D values (~ 0.5-1.5 × 10(-10) cm(2)/s) of Na(+) are higher than those (< 1 × 10(-11) cm(2)/s) of Li(+) in layered LiCoO2.We further found that the activation energy (ED ~ 0.4 eV) for the Na(+) diffusion is significantly low in these layered cobalt oxides.We found a close relation between the relative capacity and the renormalized discharge rate ( = L(2)/DT, where L and T are the film thickness and discharge time, respectively).

View Article: PubMed Central - PubMed

Affiliation: Fucalty of Pure and Applied Science, Univ. of Tsukuba, Tsukuba 305-8571, Japan.

ABSTRACT
Sodium ion secondary battery (SIB) is a low-cost and ubiquitous secondary battery for next-generation large-scale energy storage. The diffusion process of large Na(+) (ionic radius is 1.12 Å), however, is considered to be slower than that of small Li(+) (0.76 Å). This would be a serious disadvantage of SIB as compared with the Lithium ion secondary battery (LIB). By means of the electrochemical impedance spectroscopy (EIS), we determined the diffusion constant (D) of Na(+) in thin films of O3- and P2-type NaCoO2 with layered structures. We found that the D values (~ 0.5-1.5 × 10(-10) cm(2)/s) of Na(+) are higher than those (< 1 × 10(-11) cm(2)/s) of Li(+) in layered LiCoO2. Especially, the D values of O3-NaCoO2 are even higher than those of P2-NaCoO2, probably because O3-NaCoO2 shows successive structural phase transitions from the O3, O'3, P'3, to P3 phases with Na(+) deintercalation. We further found that the activation energy (ED ~ 0.4 eV) for the Na(+) diffusion is significantly low in these layered cobalt oxides. We found a close relation between the relative capacity and the renormalized discharge rate ( = L(2)/DT, where L and T are the film thickness and discharge time, respectively).

No MeSH data available.


Related in: MedlinePlus