Crystallization-induced ultrafast Na-ion diffusion in nickel hexacyanoferrate for high-performance sodium-ion batteries

Journal Pre-proof Crystallization-Induced Ultrafast Na-Ion Diffusion in Nickel Hexacyanoferrate for HighPerformance Sodium-Ion Batteries Yue Xu, Mingyang Ou, Yi Liu, Jia Xu, Xueping Sun, Chun Fang, Qing Li, Jiantao Han, Yunhui Huang PII:

S2211-2855(19)30957-7

DOI:

https://doi.org/10.1016/j.nanoen.2019.104250

Reference:

NANOEN 104250

To appear in:

Nano Energy

Received Date: 12 February 2019 Revised Date:

21 October 2019

Accepted Date: 30 October 2019

Please cite this article as: Y. Xu, M. Ou, Y. Liu, J. Xu, X. Sun, C. Fang, Q. Li, J. Han, Y. Huang, Crystallization-Induced Ultrafast Na-Ion Diffusion in Nickel Hexacyanoferrate for High-Performance Sodium-Ion Batteries, Nano Energy, https://doi.org/10.1016/j.nanoen.2019.104250. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Crystallization-Induced Ultrafast Na-Ion Diffusion in Nickel Hexacyanoferrate for High-Performance Sodium-Ion Batteries Yue Xua, Mingyang Ou, Yi Liu, Jia Xu, Xueping Sun, Chun Fang*, Qing Li, Jiantao Han*, and Yunhui Huang a

State Key Laboratory of Material Processing and Die & Mould Technology, School of

Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China

Abstract Prussian blue analogues (PBAs) have attracted great interests due to their stable and open framework structures as novel electrode materials in rechargeable sodium-ion batteries (SIBs). However, Na+ diffusion within electrode materials not only relates to many confined spaces formed by lattice frameworks for Na-ion storage but also highly involves with Na+ migration channel generated by lattice periodic arrangement. In this work, the correlation between PBAs crystallinity and Na+ insertion/extraction properties were systematically investigated. Highcrystallized nickel hexacyanoferrate (NiHCF-h) exhibits a fast Na-ion migration process with a high diffusion coefficient of 8.1×10-10 cm-2 s-2, and a high capacity retention of 73.7% at 4.25 A

*

Corresponding author. Tel. & fax: 86-27-87558241. E-mail: [email protected] (J. Han), [email protected] (C. Fang)

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g-1. Even crystal size is six times larger than low-crystallized nickel hexacyanoferrate (NiHCF-l), the high-crystallized NiHCF-h shows a faster Na+ insertion/extraction process. The basic structural characterization and pair distribution function (PDF) analysis show that NiHCF-h has a long-range lattice periodicity, enabling Na ions transfer more easily through migration channels. This demonstrates that the crystallinity of PBAs is an extremely important factor in ionic migration process, even with proved vacancies and H2O molecules in PBAs framework structure. Keywords: Sodium-Ion Battery; High-Rate Performance; Na-Ion Migration; Pair Distribution Function Analysis.

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1. Introduction With the increasing demand for renewable energy and limited lithium resource, it is quite important to develop new type of rechargeable batteries.[1] Sodium-ion batteries (SIBs) are suitable candidates for large-scale electrical energy storage (EES) systems due to abundant resource of sodium and low cost.[2-6] Prussian blue analogues (PBAs) with large interstitial sites (~4.6 Å) and spacious migration channels (~3.2 Å in [100] direction) are appropriate for the occupancy and migration of Na ions.[7-13] Generally, PBAs can be simply described as AxM[Fe(CN)6]y•□1-y·mH2O (□: [Fe(CN)6] vacancies, M: transition metal, and A: alkali cations).[14-16] Imperfections in PBAs frameworks may lead to capacity fading and low coulombic efficiency,[17, 18] which are mainly owing to lattice missing, framework collapsing, and side reactions between organic electrolyte and coordinated H2O molecules in framework structure.[19, 20] Therefore, the recent researches of PBAs are focused on controllable synthesis to pursue for low defect and high quality.[21-25] However, both [Fe(CN)6] vacancies and H2O molecules are intrinsic characteristics for PBAs framework. Due to these characteristics, PBAs have

been

studied

for

some

other

applied

purposes,

such

as

humidity-induced

magnetization/magnetic pole inversion[26], Zn-ion insertion, and exchange between cavity sites and vacant sites,[27] etc. Na+ diffusion in crystal phase not only depends on crystal lattice that provides Na-ion occupation sites, but also relates to Na+ migration channel generated by framework periodic arrangement. Besides vacancies and H2O molecules in PBAs lattice, a smooth Na-ion diffusion pathway is a significant factor for the whole electrochemical performance of SIBs. In this work, we demonstrate the effect of PBAs crystallinity on Na+ insertion/extraction process. The high-crystallized sample (NiHCF-h) and low-crystallized sample (NiHCF-l) with

3

almost the same vacancy and H2O content are compared. The crystal size of NiHCF-h is six times larger than NiHCF-l. As we know, reducing crystal size generally helps to enhance the rate performance due to the shortened ion diffusion distance.[28] Unexpectedly and interestingly, the NiHCF-h with much larger crystal size shows a faster insertion/extraction process for Na-ion diffusion. It exhibits a large specific capacity of 78.0 mAh g-1 at a current density of 17 mA g-1, and the capacity retains up to 57.5 mAh g-1 even at 4.25 A g-1. Moreover, it presents a fast Na+ion conduction with high diffusion coefficient (DNa) of 8.1×10-10 cm-2 s-2, which can be ascribed to high-quality crystal structure with fine periodicity lattice and smooth migration channels for Na-ion transportation confirmed by pair distribution function (PDF) analysis. In addition, a full cell with NiHCF-h as cathode and hard carbon as anode presents a quite stable cycle performance, suggesting a great potential for EES applications. 2. Experimental section 2.1 Material Synthesis. NiHCF-h and NiHCF-l were synthesized by a simple coprecipitation method. 1 mmol NiCl2‧6H2O and 1 mmol Na4P2O7 were added into 20 ml distilled water to form solution A under constantly stirring. Meanwhile 1 mmol K3Fe(CN)6, 0.1 g PVP, and 10 mmol NaCl were added into 50 ml water under constantly stirring to form solution B. After dropwise adding solution A into solution B, the mixture aged for 24h. With control crystallization process by Na4P2O7 chelation, high-crystallized NiHCF-h was obtained. Low-crystallized NiHCF-l was synthesized as the same process as NiHCF-h, but without Na4P2O7 controlling. All the chemicals were of analytical-grade and purchased from Aladdin China. Hard carbon anode used in full cells was purchased from SCM Industrial Chemical Co., Ltd.

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2.2 Material Characterization Crystal structure of NiHCFs was investigated by X-ray diffraction with Cu Kα radiation (XRD, Panalytical X’pert PRO MRD). The microstructure and crystal structure were characterized by field-emission scanning electron microscopy (FE-SEM, VEGA 3 SBH) and transmission electron microscopy (TEM, Tecnai G2 F30 S-TWIN, FEI). Netzsch STA 449F3 analyzer was employed to take the thermogravimetry (TG) measurements. Raman scattering spectra of the samples were detected with the excitation wavelength of 532 nm by LabRAM HR800 (Horiba Jobin Yvon). The compositions of the samples were determined by AAS (Atomic Absorption Spectroscopy) detection (GBC AVANTA M, Australia). NiHCF powders were firstly heated at 500 °C for 2 h in air, then dissolved in mixed solution of HCl and HNO3 (v/v = 2:1), and finally determined by AAS. 2.3 X-ray Total Scattering Experiments Panalytical X’pert PRO MRD with Ag Kαradiation and a GaliPIX3D detector were used for pair distribution function (PDF) analysis in the range from 2° to 150° in 24 hours with the wavelength of 0.559 Å. The raw data of total scattering diffraction were changed into PDF patterns in X’Pert HighScore Plus software by Fourier transformation with a Qmax of 21.6 Å-1. And PDFgui program was used for simulating PDF data.[29] 2.4 Electrochemical Measurements Electrochemical properties were measured on CR2032 coin cells, all of them were assembled in an argon-filled glovebox. For electrode manufacture, active material (70 wt%), ketjen black (20 wt%), and polytetrafluoroethylene (PTFE) binder (10 wt%) were mixed together, rolled into

5

thin film and dried at 100°C for 12 hours. According to the cutting tool with a diameter of 8 mm, and weight of each electrode is approximately 4 ± 0.2 mg, the areal mass loading of active materials is determined as 5.5 ± 0.3 mg cm-2. Finally, electrodes were pressed onto aluminum meshes. Ethylene carbonate (EC)/diethyl carbonate (DEC) (v/v = 1:1) and fluoroethylene carbonate (FEC 2 wt%) with 1 M NaClO4 was used as electrolyte. The separator was glass fiber (GF/A) purchased from Whatman. In the half cells, metallic sodium acted as counter electrode. The galvanostatic charge/discharge tests were carried out in the range of 2.0 V - 4.2 V versus Na+/Na on a battery testing system (BTS 3000n, Neware Technology Co., China). Cycle voltammetry (CV) was measured in the same range of 2.0 V - 4.2 V on an electrochemical workstation (CHI 600E, China). Before full-cell fabrication, HC anodes were pre-inserted by Na. For anode electrodes, 80 wt% HC, 10 wt% super P, and 10 wt% polyvinylidene fluoride (PVDF) binder were mixed uniformly in 3-methyl-pyrrolidone (NMP). Then the mixture was coated onto a copper foil and dried at 80 °C to achieve HC anode.[30] 3. Results and Discussion The purity and crystallinity of the two NiHCF samples are examined by X-ray diffraction (XRD) analysis shown in Fig. S1a. All the peaks indexed to a face-centered cubic phase (JCPDS Card No. 52-1907). The stronger intensity and sharper diffraction peaks indicate better crystallinity of the sample, which was synthesized by Na4P2O7 controlling process (the orange curve in Fig. S1). The high-crystallized sample is named as NiHCF-h, and the low-crystallized sample is marked as NiHCF-l. The Rietveld refinement (Fig. 1a) shows that NiHCF-h exhibits a cubic structure with lattice parameter a = 10.226 Å. The corresponding local structure of NiHCFh is shown in Fig. 1b. The low-spin Fe ions are coordinated to carbon atoms, the Ni ions are linked with nitrogen atoms, and the NiHCF framework structure is built with Fe(III)-C≡N-Ni(II)

6

skeletons.[31] In the Raman spectra (Fig. S1b), the band located at 2184 cm-1 is assigned to the vibration of Fe(III)-C≡N-Ni(II).[32] For FT-IR spectra (Fig. S1c), the adsorption peak located at 2162 cm-1 belongs to the stretch mode of ν(CN) coordinate to Fe(III).[33] The adsorption peaks located at 1620 and 3550 cm-1 are associated with O-H stretch and H-O-H bend modes, respectively, from interstitial water. The peak located at 3617 cm-1 are from free surface water.[34] TGA results are shown in Fig. S1d. The first-step weight loss below 180 °C corresponds to absorbed surface water, while the second-step weight loss between 180 − 280 °C is due to the coordinated water. When the temperature arises up to 400 °C, the NiHCF frameworks begin to collapse (Fig. S2).[34] Combining TGA and atomic absorption spectroscopy (AAS,

Table

S1)

results,

the

chemical

composition

can

be

determined

as

Na0.22Ni[Fe(CN)6]0.76‧3.67H2O and Na0.27Ni[Fe(CN)6]0.77‧4.41H2O for NiHCF-h and NiHCF-l (Table 1), respectively. The [Fe(CN)6] vacancy contents in the two samples are almost same. Calculation by Scherrer formula reveals that the crystal size of NiHCF-h is 113.2 nm, which is six times larger than that of NiHCF-l (17.9 nm), as shown in Table 1. Fig. 1 displays their SEM and TEM images. The NiHCF-h prepared with Na4P2O7 presents uniform particles with regular squared shape and fine edge, which mean size is around 150 nm, while the NiHCF-l is composed of irregular nanoparticles (Fig. S4). The charge/discharge curves of NiHCF-l and NiHCF-h are shown in Fig. 2a, b at a current density of 17 mA g-1. For the first cycle, the coulombic efficiencies of NiHCFs are below 100%, which is due to low Na-content and some side reactions with interstitial water in the framework structure.[35,

36]

Apart from the activation process at the first cycle, the following

charge/discharge curves are almost unchanged, indicating a highly reversible electrochemical process. The specific capacity of NiHCF-h (78.0 mAh g-1) is higher than NiHCF-l (68.7 mAh g-

7

1

). Cyclic voltammetry (CV) curves were present as a pair of well-defined and symmetric peaks

attributed to FeIII/II redox couple (inset of Fig. 2). The redox polarization of NiHCF-h is lower than NiHCF-l, indicating a faster kinetics model for Na+ insertion/extraction.[23, 37] The rate performances are shown in Fig. 2c, d. The NiHCF-h exhibits a superior rate performance with discharge capacities of 78.0, 76.7, 75.6, 73.7, 71.0, 65.8, 63.8, 62.1, 59.7, and 57.5 mAh g-1 at the rates of 0.2, 0.5, 1, 2, 5, 10, 20, 30, 40, and 50 C, respectively. The capacity retention reaches 73.7% at 50 C compared to 0.2 C. When the current density returns to 10 C, the capacity can recover to 64.8 mAh g-1, suggesting an excellent reversibility. The NiHCF-h presents better rate performance than low-crystallized one, indicating faster Na+ insertion/extraction process. Compared with the previous reports, NiHCF-h exhibits a competitive rate performance (see Table S2). Fig. 2e presents the cycling performance of NiHCFs at a current density of 300 mAh g-1. Although there are around 23% Fe(CN)6 vacancies and a certain amount of H2O molecules in NiHCFs, they present ultra-stable cycling performance with about 97.3% retention over 1200 cycles (Fig. S6), and it remains cubic phase without any phase transformation during redox reactions (Fig. S7). In previous reports, the introduction of Ni could stabilize the Fe-C≡N-Ni bonds and favor the electronic shuttling, that makes the both NiHCFs present good rate performance and cyclic stability.[38-40] In this work, the significant enhancement of NiHCF-h in rate performance and specific capacity should be attributed to the high-crystallinity and uniform particles. A detailed structural information is obtained from Rietveld analysis to understand disorder and distortion in the frameworks.[41] X-ray scattering PDF measures atom-atom correlations to directly probe local structure around specific atoms or sites.[42] The PDF analysis of the pristine NiHCF with different crystallinity samples is shown in Fig. 3. The assignments of PDF curves

8

are determined from the simulated structure of NiHCF shown in Fig. S8. In a short range of 1 - 7 Å, there is not obvious coordination difference between the two samples, indicating a similar average local structure in the range of single lattice for Na+ occupancy. This could be due to the approximate components of the two samples (Table 1) that makes the similar skeletons. While at a large range (r ＞ 7 Å), the weak peak intensity of NiHCF-l indicates a coordination decrease, which reveals the loss of lattice periodicity. At the longer distance (10 - 40 Å, Fig. 3b), the difference between the two curves increases. The reduced peak intensity of NiHCF-l reveals a poor periodicity and a smaller lattice dimension, which is caused by the low crystallinity and consistent with the Scherrer calculation results (see Table 1). The ionic diffusion not only relates to the single-crystal lattice that provides Na-ion occupancy[43] but also depends on the ionic migration channel generated by the lattice periodic arrangement. Here, PDF analysis shows that NiHCF-l has a poor lattice ordering and weak periodicity, which could block its ionic migration channel. Electrochemical active materials are always designed as nano-dimension to enhance specific surface area and increase the contact with electrolyte for a higher power and rapider charging process.[44-46] In this work, the high-crystallized NiHCF-h with larger crystal size presents a rapid intercalation/extraction process. According to the PDF analysis, the high-crystallized structure with a long-range lattice periodicity, as seen in Fig. 4a, provides smooth solid-state ionic diffusion pathway, Na ions can transfer through the framework channels of PBAs without obstruction. While in low-crystallized frameworks, the poor lattice ordering leads to the deficiency of lattice periodicity, which will block the ionic migration channel and hence result in a restricted ionic diffusion process. Also, the poor periodicity will increase the number of surface atoms This could decrease the occupancy sites of Na ions from host lattice built by the limited

9

atoms, leading to low capacities. Furthermore, CV curves at different scan rates from 0.1 to 1.0 mV s-1 are employed to determine the solid-state diffusion kinetics of Na ions (Fig. 5). The peak current (ip) increases with scan rate rising. Na-ion diffusion coefficient (DNa) can be estimated according to the equation: ip = 2.69×105 n3/2A DNa1/2ν1/2Co

(1).

Where ip is the peak current (mA), n is the number of electrons (1.0 per reaction species for Na), A is the area between both electrodes (~ 0.25 cm2), Co the concentration of Na ions (mol cm-3), and ν the scan rate. Based on the above equation, ip shows a linear relationship with ν1/2. The calculated insertion diffusion coefficients DNa are 8.10 × 10-10 and 4.50 × 10-10 cm-2 s-2 for highcrystallized and low-crystallized NiHCF, respectively, demonstrating that the kinetics for Na-ion diffusion in NiHCF-h is faster. The EIS spectra are measured at a dissociated state. The high/middle frequency semicircles are ascribed to the charge transfer resistance (Rct) and its corresponding constant-phase angle element (CPE2) at the electrode/electrolyte. The Rct values are high for both samples, which may be caused by the structure imperfection in the frameworks as Fe(CN)6 vacancies and inherent H2O molecules.[47] The Rct of NiHCF-l is larger than NiHCF-h, revealing a slower kinetics of the Faradic reaction for NiHCF-l[48, 49], which is consistent with the above CV results. Low frequency oblique line is attributed to Warburg impedance (Wo), which is response to the Na-ion solid state diffusion within NiHCFs. There are less differences on Wo between the two samples, that is due to the decreased particle size of NiHCF-l. The effect of reducing crystallinity of NiHCF-l on diffusion is compensated by the increasing capacitive behavior of bounded diffusion.[50] Briefly, the high-crystallized NiHCF framework with a long-range ordering provides smooth and continuous migration channel, and guarantees a fast Na-ion diffusion process.

10

For practical applications, full-cells with NiHCF-h cathode and hard carbon (HC) anode were fabricated, as shown in Fig. 6. The mass ratio of hard carbon anode to NiHCF cathode was 1, to offer a stable charge/discharge platform for the full-cells, only platform part of the hard carbon served in redox reactions. The full-cells were operated within a voltage range of 1.8 - 3.7 V matching with the charge/discharge galvanostatic profile (Fig. 6a). At a current density of 17 mA g-1 (0.2 C), it gives a high capacity as 84 mAh g-1 (based on the mass of active NiHCF-h), and the capacity retains to 69.2 mAh g-1 at 5 C rate (＞80% capacity retention). NiHCF-h cooperates well with HC, and the full cell exhibits great cycling stability at the current density of 85 mA g-1 over 250 cycles. After an activation process, the coulombic efficiency approaches 100%, which suggests a reversible chemical reaction. 4. Conclusions In summary, the crystallinity is a significant factor in PBAs for Na+ migration process. Highcrystallized NiHCF-h and low-crystallized NiHCF-l are synthesized by a simple co-precipitation method. The Fe(CN)6 vacancies and H2O contents in the two samples are almost the same. They exhibit superior cyclic stability over 1200 cycles. And NiHCF-h shows a better electrochemical performance, even crystal size of NiHCF-h is six times larger than NiHCF-l. For the highcrystallized NiHCF, the specific capacity is 78 mAh g-1 at 17 mA g-1, and retains to 57.5 mAh g-1 at 4.25 A g-1. In addition, NiHCF-h also presents a fast Na migration process with a high Na-ion diffusion coefficient (DNa) of 8.1×10-10 cm-2 s-2. Based on PDF analysis, high-crystallized NiHCF-h has a long-range lattice periodicity, leading to a smooth and continuous diffusion pathway for Na-ion migration. Crystallinity is one of the most significant factors for Na-ion migration process, even with vacancies and H2O molecules in PBAs frameworks. Furthermore,

11

the full cell of NiHCF-h exhibits excellent rate and cyclic performance, showing a high potential application.

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant Nos. 51632001, 51702111, 51772117, and 51902118), and the National Key Research and Development Plan of China (Grant Nos. 2016YFB010030X and 2016YFB0700600). The authors also thank the State Key Laboratory of Materials Processing and Die & Mould Technology of HUST, and the Analytical Testing Centre of HUST for Raman, XRD, SEM, TEM, TGA, and other measurements.

Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/xx.xxxx/j.nanoen.xxxx.xx.xxx.

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References [1] S. Chu, Y. Cui, N. Liu, Nat. Mater., 16 (2016) 16. [2] K.J. Griffith, K.M. Wiaderek, G. Cibin, L.E. Marbella, C.P. Grey, Nature, 559 (2018) 556. [3] J.-Y. Hwang, S.-T. Myung, Y.-K. Sun, Chem. Soc. Rev., 46 (2017) 3529-3614. [4] H. Hou, C.E. Banks, M. Jing, Y. Zhang, X. Ji, Adv. Mater., 27 (2015) 7861-7866. [5] A. Eftekhari, D.-W. Kim, J. Power Sources, 395 (2018) 336-348. [6] X. Zheng, C. Bommier, W. Luo, L. Jiang, Y. Hao, Y. Huang, Energy Storage Materials, 16 (2019) 6-23. [7] J. Zhang, T. Liu, X. Cheng, M. Xia, R. Zheng, N. Peng, H. Yu, M. Shui, J. Shu, Nano Energy, 60 (2019) 340-361. [8] Y. Huang, M. Xie, Z. Wang, Y. Jiang, Q. Huang, X. Bai, L. Li, F. Wu, R. Chen, Nano Energy, 60 (2019) 294-304. [9] K. Hurlbutt, S. Wheeler, I. Capone, M. Pasta, Joule, 2 (2018) 1950-1960. [10] R. Zhao, Z. Liang, R. Zou, Q. Xu, Joule, 2 (2018) 2235-2259. [11] L. Niu, L. Chen, J. Zhang, P. Jiang, Z.P. Liu, J. Power Sources, 380 (2018) 135-141. [12] Q. Yang, W. Wang, H. Li, J. Zhang, F.Y. Kang, B.H. Li, Electrochim. Acta, 270 (2018) 96103. [13] H.C. Gao, S. Xin, L.G. Xue, J.B. Goodenough, Chem, 4 (2018) 833-844. [14] A. Ludi, H.U. Güdel, Struct. Bond., 14 (1973) 1-21. [15] H.J. Buser, D. Schwarzenbach, W. Petter, A. Ludi, Inorg. Chem., 16 (1977) 2704. [16] Q. Zhang, L. Fu, J. Luan, X. Huang, Y. Tang, H. Xie, H. Wang, J. Power Sources, 395 (2018) 305-313. [17] T. Shibata, Y. Moritomo, Chem. Commun., 50 (2014) 12941-12943.

13

[18] M. Takachi, Y. Fukuzumi, Y. Moritomo, Dalton Trans., 45 (2016) 458-461. [19] Y. You, X.L. Wu, Y.X. Yin, Y.G. Guo, Energy Environ. Sci., 7 (2014) 1643-1647. [20] R.Y. Wang, B. Shyam, K.H. Stone, J.N. Weker, M. Pasta, H.W. Lee, M.F. Toney, Y. Cui, Adv. Energy Mater., 5 (2015) 1401869. [21] X. Wu, Y. Luo, M. Sun, J. Qian, Y. Cao, X. Ai, H. Yang, Nano Energy, 13 (2015) 117-123. [22] X. Wu, C. Wu, C. Wei, L. Hu, J. Qian, Y. Cao, X. Ai, J. Wang, H. Yang, ACS Appl. Mater. Interfaces, 8 (2016) 5393-5399. [23] X.Y. Wu, M.Y. Sun, S.M. Guo, J.F. Qian, Y. Liu, Y.L. Cao, X.P. Ai, H.X. Yang, Chemnanomat, 1 (2015) 188-193. [24] R. Chen, Y. Huang, M. Xie, Z. Wang, Y. Ye, L. Li, F. Wu, ACS Appl. Mater. Interfaces, 8 (2016) 31669-31676. [25] Y. Liu, Y. Qiao, W. Zhang, Z. Li, X. Ji, L. Miao, L. Yuan, X. Hu, Y. Huang, Nano Energy, 12 (2015) 386-393. [26] S.I. Ohkoshi, K.I. Arai, Y. Sato, K. Hashimoto, Nat. Mater., 3 (2004) 857-861. [27] V. Renman, D.O. Ojwang, M. Valvo, C.P. Gómez, T. Gustafsson, G. Svensson, J. Power Sources, 369 (2017) 146-153. [28] Y. Mao, Y. Chen, J. Qin, C. Shi, E. Liu, N. Zhao, Nano Energy, 58 (2019) 192-201. [29] B. Zhang, T. Zhu, M. Ou, N. Rowell, H. Fan, J. Han, L. Tan, M.T. Dove, Y. Ren, X. Zuo, S. Han, J. Zeng, K. Yu, Nat. Commun., 9 (2018) 2499. [30] C.M. Ghimbeu, J. Gorka, V. Simone, L. Simonin, S. Martinet, C. Vix-Guterl, Nano Energy, 44 (2018) 327-335. [31] D. Kim, T. Hwang, J.M. Lim, M.S. Park, M. Cho, K. Cho, PCCP, 19 (2017) 10443-10452. [32] Y. You, X.L. Wu, Y.X. Yin, Y.G. Guo, J. Mater. Chem. A, 1 (2013) 14061-14065.

14

[33] Z. Ji, B. Han, H. Liang, C. Zhou, Q. Gao, K. Xia, J. Wu, ACS Appl. Mater. Interfaces, 8 (2016) 33619-33625. [34] J. Song, L. Wang, Y. Lu, J. Liu, B. Guo, P. Xiao, J.-J. Lee, X.-Q. Yang, G. Henkelman, J.B. Goodenough, J. Am. Chem. Soc., 137 (2015) 2658-2664. [35] Y. You, X. Yu, Y. Yin, K.-W. Nam, Y.G. Guo, Nano Res., 8 (2015) 117-128. [36] Y. Yang, E. Liu, X. Yan, C. Ma, W. Wen, X.Z. Liao, Z.F. Ma, J. Electrochem. Soc., 163 (2016) A2117-A2123. [37] V.B. Isfahani, N. Memarian, H.R. Dizaji, A. Arab, M.M. Silva, Electrochim. Acta, 304 (2019) 282-291. [38] P. Ge, S. Li, L. Xu, K. Zou, X. Gao, X. Cao, G. Zou, H. Hou, X. Ji, Adv. Energy Mater., 9 (2019) 1803035. [39] P. Ge, S. Li, H. Shuai, W. Xu, Y. Tian, L. Yang, G. Zou, H. Hou, X. Ji, Adv. Mater., 31 (2019) 1806092. [40] C. Li, Q. Yang, M. Shen, J.Y. Ma, B.W. Hu, Energy Storage Materials, 14 (2018) 82-89. [41] K.W. Chapman, P.J. Chupas, C.J. Kepert, J. Am. Chem. Soc., 127 (2005) 11232-11233. [42] J. Shamblin, M. Feygenson, J. Neuefeind, C.L. Tracy, F. Zhang, S. Finkeldei, D. Bosbach, H. Zhou, R.C. Ewing, M. Lang, Nat. Mater., 15 (2016) 507. [43] L. Que, F. Yu, L. Zheng, Z.-B. Wang, D. Gu, Nano Energy, 45 (2018) 337-345. [44] W. Ren, M. Qin, Z. Zhu, M. Yan, Q. Li, L. Zhang, D. Liu, L. Mai, Nano Lett., 17 (2017) 4713-4718. [45] C.H. Li, Y. Nanba, D. Asakura, M. Okubo, D.R. Talham, RSC Adv., 4 (2014) 24955-24961. [46] S. Li, P. Ge, F. Jiang, H. Shuai, W. Xu, Y. Jiang, Y. Zhang, J. Hu, H. Hou, X. Ji, Energy Storage Materials, 16 (2019) 267-280.

15

[47] D.P. Cai, X.H. Yang, B.H. Qu, T.H. Wang, Chem. Commun., 53 (2017) 6780-6783. [48] M.D. Levi, D. Aurbach, The Journal of Physical Chemistry B, 101 (1997) 4630-4640. [49] E. Barsoukov, D.H. Kim, H.S. Lee, H. Lee, M. Yakovleva, Y. Gao, J.F. Engel, Solid State Ionics, 161 (2003) 19-29. [50] J. Song, M.Z. Bazant, Phys. Rev. Lett., 120 (2018) 116001.

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Figure Captions Fig. 1. (a) The Rietveld refinement and (b) local structure of high-crystallized cubic phase NiHCF-h. The (c) SEM and (d) TEM images of NiHCF-h. Fig. 2. The charge/discharge curves of (a) low-crystallized and (b) high-crystallized NiHCF at current density of 17 mA g-1 (0.2 C). (c, d) Rate performance of NiHCF-h (orange) and NiHCF-l (purplish blue). (d) Cycling stability at a current density of 300 mA g-1. Fig. 3. PDF patterns of high/low-crystallized NiHCF samples at a range of (a) 1 – 10 Å and (b) 10 – 40 Å. Fig. 4. The illustration of the diffusion route in (a) high-crystallized and (b) low-crystallized PBAs frameworks. Fig. 5. The CV curves of (a) NiHCF-l and (b) NiHCF-h at different scan rate from 0.1 to 1.0 mV s-1. (c) The relation between the square root of the scan rate (ν1/2) and the corresponding currents for redox peaks. (d) The EIS results of NiHCF-h (orange) and NiHCF-l (purplish blue) at dissociated state. Fig. 6. Full cell electrochemical characterization. (a) potential profiles of the NiHCF-h cathode and hard carbon anode. (b) Rate performance (1 C = 85 mA g-1). (d) Cycling stability at a current density of 85 mA g-1.

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Figure 1.

Fig. 1. (a) The Rietveld refinement and (b) local structure of high-crystallized cubic phase NiHCF-h. The (c) SEM and (d) TEM images of NiHCF-h.

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Figure 2.

Fig. 2. The charge/discharge curves of (a) low-crystallized and (b) high-crystallized NiHCF at current density of 17 mA g-1 (0.2 C). (c, d) Rate performance of NiHCF-h (orange) and NiHCF-l (purplish blue). (e) Cycling stability at a current density of 300 mA g-1.

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Figure 3.

Fig. 3. PDF patterns of high/low-crystallized NiHCF samples at a range of (a) 1 – 10 Å and (b) 10 – 40 Å.

20

Figure 4.

Fig. 4. The illustration of the diffusion route in (a) high-crystallized and (b) low-crystallized PBAs frameworks.

21

Figure 5.

Fig. 5. The CV curves of (a) NiHCF-l and (b) NiHCF-h at different scan rate from 0.1 to 1.0 mV s-1. (c) The relation between the square root of the scan rate (ν1/2) and the corresponding currents for redox peaks. It is found that the peak currents for the both electrodes display a linear relation with the square root of the scan rate (ν1/2). (d) The EIS results of NiHCF-h (orange) and NiHCF-l (purplish blue) at dissociated state.

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Figure 6.

Fig. 6. Full cell electrochemical characterization. (a) potential profiles of the NiHCF-h cathode and hard carbon anode. (b) Rate performance of the full cell at various rates (1 C = 85 mA g-1). (d) Cycling stability at a current density of 85 mA g-1.

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Table 1. The synthetic condition, chemical composition (determined by AAS) and particle size of high/low-crystallized samples. Crystal size (Å) /

Sample

Synthetic conditions

Compositions

NiHCF-h

P2O74-:Ni = 1 : 1, Fe(CN)3-

Na0.22Ni[Fe(CN)6]0.76‧3.67H2O

1132

NiHCF-l

Without P2O74-, Fe(CN)3-

Na0.27Ni[Fe(CN)6]0.77‧4.41H2O

179

Scherrer Calculator

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Pair distribution function (PDF) analysis was used to to directly probe lattice periodicity of the two samples. The high-crystallized structure, with long-range lattice periodicity, provides smooth solid-state ionic diffusion pathway, exhibits a fast Na+-ion migration process. Both half-cell and full-cell with high-crystallized NiHCF cathode exhibit excellent rate and cyclic performances for Na+-ion batteries.

Author Information:

Yue Xu received her Ph.D. degree at Institute of Solid Physics, Chinese Academy of Sciences. Presently, she is a postdoctoral researcher at School of Materials Science and Engineering, Huazhong University of Science and Technology. Her research is focused on energy storage materials for secondary batteries.

Mingyang Ou obtained his bachelor degree (2016) in college of physics, Jilin University. And then he joined Professor Han’s group as a Ph.D. candidate at school of materials science and engineering in Huazhong University of Science & Technology. His research interests include local structure exploring and structure properties relationship understanding inside batteries by the application of X-ray based techniques.

Yi Liu is a Ph.D. candidate under the supervision of Prof. Jiantao Han at School of Materials Science and Engineering in Huazhong University of Science and Technology. He received his BSc (2011) and MSc (2014) degree in Wuhan Institute of Technology. His current research focused on aqueous rechargeable batteries and devices.

Jia Xu is a Ph.D. candidate under the supervision of Prof. Jiantao Han at the School of Materials Science and Engineering in Huazhong University of Science and Technology. He received his B.Eng. degree at Huazhong University of Science and Technology in 2018. His current research focuses on Pair Distribution Functions analysis and controllable synthesis of graphene.

Xueping Sun received her Ph.D. degree in Shanghai Institute of Applied Physics, Chinese Academy of Science in 2017. Currently, she is conducting postdoctoral research at School of Materials Science and Engineering, Huazhong University of Science and Technology. Her main research interests focus on the structure-activity relationship of non-precious metal electrocatalysts in PEM fuel cells and Zn-air batteries based on XAFS techniques.

Chun Fang received her Ph.D. from Fudan University in 2008. She then worked as a senior engineer at Evergreen Solar Corp. from 2009 to 2012. After that, she was an R&D manager at Enpower Energy Corp. from 2012 to 2015. Currently, she is researcher associate in Huazhong University of Science and Technology. Her research interests focus on new materials for energy storage applications.

Qing Li is a professor of School of Materials Science and Engineering in Huazhong University of Science and Technology (HUST), China. He received his Ph.D. in Chemistry from Peking University in 2010 and then worked as a postdoctoral research associate consecutively at Los Alamos National Laboratory (2011–2013) and Brown University (2013–2015). He joined HUST as a full professor in 2016. His research interests include functional nanomaterials and their applications in electrocatalysis, PEM fuel cells and batteries.

Jiantao Han is a professor of School of Material Science and Engineering in Huazhong University of Science and Technology (HUST), China. He received his Ph.D. in Chemistry from Fudan University in 2007 and then worked at UT Austin (2007-2010), Los Alamos National Laboratory (2010-2012( and Pellion Tech. (20122014). He jointed HUST as a full professor in 2016. His research interests include atomic distribution function (PDF) analysis and Li-ion batteries.

Dr. Yunhui Huang received his BSc, MSc and PhD from Peking University. In 2000, he worked as a postdoctoral researcher in Peking University. From 2002 to 2004, he worked as an associate professor in Fudan University and a JSPS fellow at Tokyo Institute of Technology, Japan. He then worked in the University of Texas at Austin for more than three years. In 2008, he became a chair professor of materials science in Huazhong University of Science and Technology. His research group works on batteries of energy storage and conversion. For details please see the lab website: http://www.sysdoing.com.cn.

Declaration of Interest Statement All the authors declare no conflict of interest.