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Journal of Materials Chemistry A
Page 8 of 9
Journal Name
PAPER
process (b-f), the (002) peak belonging to α -KVOPO gradually with 86.8% capacity retention over 100 cycles Vaietw A0r.ti5clCe Oanlninde
I 4
disappears with the appearance of new peaks, which can be superior rate capability of 73% retentionDOaIt: 1200.1C0.39It/sC9rTeAla0t3i1v9e2lHy
4 4
identified to be (002) peak of αII-K1-xVOPO . And the (002) peak good rate capability in PIBs is better than other VOPO -based
gradually shifts to the lower 2θ angle, indicating a solid materials in LIBs and SIBs. Furthermore, a high contribution of
solution process and the expansion of the interlayer spacing as capacitive charge storage explored by cyclic voltammetry
the extraction of K ions, because K ions can enhance the reveals the special intercalation pseudocapacitive mechanism.
coordination reaction of the stacked layer and make the Ex-situ XRD measurements indicate a reversible structural
1
1,36
interlayer spacing smalle.
peak slightly shifts to the higher 2θ angle, indicating that the insertion/extraction, and the volume change is only 9.4%. This
potassium ions are extracted between the two VOPO layers. work demonstrates that layered KVOPO is a promising
The discharge process (f-j) is an inverse process of charge (a-f), candidate for PIBs.
however, KVOP-NS cannot recover to αII-KVOPO after being
fully discharged. Thus, we believe that αII-KVOPO at the full
potassiation stage is metastable at room temperature. The
phase transformation between α - and αII-KVOPO seems facile
Unlike the (002) peak, the (200) evolution between
α
I
-
and
α
II-KVOPO
4
during K ions
4
4
4
4
Acknowledgements
I
4
This study was supported by the National Science Foundation
of China (NSAF U1630106, grant nos. 21875237, 51577175)
and National Key R&D Program of China (grant no.
no matter during the synthesis or electrochemical process,
possibly due to the very similar layered structures. Fig. 5e and
f show the variation tendency of the lattice parameters, and
5
2
018YFB0905400). We are also grateful to Elementec Ltd in
the total volume change calculated is 9.4%, which is close to
Suzhou for its technical support.
2
2
4
that of layered-NaVOPO in SIBs (8.8%) but less than
3
6
V
2
O
5
·0.6H O in PIBs (~17%). Fig. S10a compares the ex-situ
2
st
nd
XRD patterns of KVOP-NS at the 1 and 2 cycles. The similar References
XRD patterns at charge and discharges states indicate the
1
S. Komaba, T. Hasegawa, M. Dahbi, K. Kubota, Electrochem.
same redox mechanism and good electrochemical reversibility.
The ex-situ XRD patterns of L-KVOP samples after 100 cycles
are shown in Fig. S10b. The characteristic (002) peak of the
layered structure is maintained, except a new peak at about
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X. Wu, D. P. Leonard, X. Ji, Chem. Mater., 2017, 29, 5031.
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We further compare the voltage-capacity-energy density of
our layered KVOPO
4
with polyanionic cathodes for PIBs
reported in literature in Fig. 6a. With a high operating voltage
of 3.65 V and capacity of ~115 mAh/g at 0.2C, the layered
4
delivers a competitive energy density of 420 Wh/kg
among the polyanionic cathode materials.
KVOPO
8
,11,26,37-41
The
detailed information of electrochemical section of these 7 J.-Y. Hwang, J. Kim, T.-Y. Yu, S.-T. Myung, Y.-K. Sun, Energy
cathodes is shown in Table S2, the L-KVOP delivers moderate
Environ. Sci., 2018, 11, 2821.
cycling stability, and the highest initial coulombic efficiency, 8 H. Kim, D.-H. Seo, M. Bianchini, R. J. Clément, H. Kim, J. C. Kim,
due to the optimized electrolyte. Fig. 6b illustrates the rate
Y. Tian, T. Shi, W.-S. Yoon, G. Ceder, Adv. Energy Mater., 2018,
comparison of layered KVOPO for PIBs with various layered
4
8
, 1801591.
VOPO and AVOPO
(A=Li, Na) for LIBs and SIBs.19,22-24,42
KVOPO exhibits inferior specific capacity at low rates, which is
ascribed to the high atomic weight of K. Nevertheless, the
capacity retention ratio of KVOPO is higher than that of LIBs
and SIBs at high rates, as a common result of (i) the larger
4
4
9
1
Y.-H. Zhu, Q. Zhang, X. Yang, E.-Y. Zhao, T. Sun, X.-B. Zhang, S.
Wang, X.-Q. Yu, J.-M. Yan, Q. Jiang, Chem, 2019, 5, 168.
0 T. Masese, K. Yoshii, Y. Yamaguchi, T. Okumura, Z. D. Huang,
M. Kato, K. Kubota, J. Furutani, Y. Orikasa, H. Senoh, H.
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2
2 N. Dupré, G. Wallez, J. Gaubicher, M. Quarton, J. Solid State
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3 G. He, A. Huq, W. H. Kan, A. Manthiram, Chem. Mater., 2016,
4
4
interlayer spacing of KVOPO
4
(5.94 Å, α
(4.51 Å, α
enhances diffusion kinetics across the
electrolyte/electrode interface, and (iii) the nanosheets
morphology benefits for electron and ion transport.
I
) than NaVOPO
) , (ii) the lower desolvation
4
(5.12
1
1
1
2
2
42
I
Å, α )
and LiVOPO
4
I
019, 55, 659.
+
energy of
K
2
8, 1503.
Conclusions
14 Y.-C. Lin, M. F. V. Hidalgo, I.-H. Chu, N. A. Chernova, M. S.
Whittingham, S. P. Ong, J. Mater. Chem. A, 2017, 5, 17421.
4
In summary, three layered KVOPO materials with different
1
5 B. Wen, Q. Wang, Y. Lin, N. A. Chernova, K. Karki, Y. Chung, F.
Omenya, S. Sallis, L. F. J. Piper, S. P. Ong, M. S. Whittingham,
Chem. Mater., 2016, 28, 3159.
morphologies have been synthesized and characterized in PIBs.
The optimal KVOP-NS sample exhibits superior K-storage
performance, including high average voltage (3.65 V), high
capacity (~115 mAh/g at 0.2C), considerable cycling stability
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