In Situ FTIR-Assisted Synthesis of Nickel Hexacyanoferrate Cathodes

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In-situ FT-IR Assisted Synthesis of Nickel Hexacyanoferrate Cathodes for Long-Life Sodium-Ion Batteries Yue Xu, Miao Chang, Chun Fang, Yi Liu, Yuegang Qiu, Mingyang Ou, Jian Peng, Peng Wei, Zhi Deng, Shixiong Sun, Xueping Sun, Qing Li, Jiantao Han, and Yunhui Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10312 • Publication Date (Web): 31 Jul 2019 Downloaded from pubs.acs.org on August 1, 2019

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ACS Applied Materials & Interfaces

In-situ

FT-IR

Assisted

Synthesis

of

Nickel

Hexacyanoferrate Cathodes for Long-Life SodiumIon Batteries Yue Xu,† Miao Chang,† Chun Fang,* Yi Liu, Yuegang Qiu, Mingyang Ou, Jian Peng, Peng Wei, Zhi Deng, Shixiong Sun, Xueping Sun, Qing Li, Jiantao Han* and Yunhui Huang.

AUTHOR ADDRESS. 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

KEYWORDS: Prussian blue analog cathode, Sodium ion batteries, In-situ FT-IR studies, Long cycle life

ABSTRACT: Prussian blue analogs (PBAs) with stable framework structures are ideal cathodes for rechargeable sodium-ion batteries (SIBs). The chelating-agent-assisted co-

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precipitate method is an effective way to obtain low-defect PBAs that can limit the appearance of too many vacancies and water molecules and achieve an optimized Nastorage performance. However, for this method, the mechanism of chelating-agentassisted synthesis is still unclear. Herein, the synthesis process of nickel hexacyanoferrate (NiHCF) has been investigated by in-situ infrared spectroscopy detection, with the results showing that the chelating agent oxalate makes the nucleation process slows down and effectively inhibits the formation of the Fe-C≡N-Ni frame in the aging process, producing highly-crystallized and low-defect NiHCF samples. The highquality NiHCF presents high specific capacity as 86.3 mAh g-1 (the theoretical value ~85 mAh g-1), an ultra-stable cyclic retention of 90% over 800 cycles, and a remarkable high capacity retention as 74.6% at a current density of 4250 mA g-1 (50 C). Particularly, the NiHCF//hard carbon full cell presents high specific energy density over 210 Wh kg-1, and an outstanding cyclic stability without obvious capacity attenuation over 1,000 cycles.

1. INTRODUCTION


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Sodium-ion batteries (SIBs), as appropriate energy storage systems for large-scale applications, have gained a lot of attention.1-3 Prussian blue analogs (PBAs), open framework hosts for Na+ ions, are attractive candidates as SIB cathode materials due to their low-cost, environmentally friendly synthesis procedure, wide migration channel, and large number of Na+-occupancy sites.4-8 Typical, PBAs formula are present as AxM[Fe(CN)6]y⋅β1-y⋅nH2O, symbol A for alkaline metal ion, symbol M for transition metal ions, and β for [Fe(CN)6] vacancies.9-10 However, electrochemical active-site Fe reduced with the increasing amount of [Fe(CN)6] vacancies, resulting in the decrease of specific capacities.11 The vacancies can be occupied by water molecules, leading to fragile frameworks that will likely collapse during Na+ insertion/extraction process, which results in poor cyclic performances.12-13 It is reported that the chelating-agent-assisted coprecipitate method is effective in adjusting the synthesis process and obtain highly crystallized PBAs with minimal defects.14 The controlled synthesis PBAs products often present enhanced electrochemical performances, such as high specific capacity, high rate, and long-life stability.12 With the variation of transition metals (M in AxM[Fe(CN)6]y⋅β1y⋅nH2O),

the complexation stability constant of the chelating agent changes, and the


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modulation mechanisms on PBA nucleation and growth also change.15-16 The appropriate chelating agents are required to match various transition metals and obtain highlycrystallized, low-vacancy PBAs. At present, the direct identification of the activation in chelating-agent-assisted synthesis remains challenging.

One of the specific characteristics of PBAs is the presence of cyanide (C≡N) linkers, which can be identified by infrared spectroscopy measurements.17-18 The cyanide stretching modes are closely related to their local environment, including the oxidation state of the center Fe ions, different kinds of transition metals, and the change of framework local symmetry caused by Na+ interactions. Recently, in-situ infrared spectroscopy was used to directly identify and quantitatively describe the catalytically active sites by operando probing their interfacial bonding environment.19 Infrared spectra are sensitive to coordinate environment of chemical bond. In the PBA synthesis process, when the Fe(CN)63-/4- group coordinates with the transition metal, charge density at the N end shifts towards the transition metal, the C≡N binding energy shifts to higher values,20-21 and the C≡N group vibration band should shift to higher wavenumbers in infrared


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spectroscopy. According to the sensitivity of C≡N to its bonding environment, in-situ Fourier-transform infrared spectroscopy (FT-IR) characterization is an effective way to monitor the formation process of PBA frameworks.

In this study, C2O42- as a chelating agent assists the coprecipitate synthesis of nickel hexacyanoferrate (NiHCF). According to the different ratios of Na2C2O4 to NiCl2 (C2O42- : Ni = 1, 2, 3), the stability constants of the coordination compounds varied. Then, NiHCF products synthesized with different control conditions were obtained. An operando detection with in-situ FT-IR was performed to analyze the reaction mechanisms of the addition of oxalate agents. The C2O42--controlled synthesis of NiHCF presents superior Na+-storage performances. In particular, NiHCF-3 exhibits a specific capacity of 86.3 mAh g-1, an excellent rate capability as capacity maintaining of 64.4 mAh g-1 at 50 C, and ultrastable characteristics with the capacity retention of 90% more than 800 redox cycles. Full cells were fabricated with a NiHCF-3 cathode and hard carbon anode. The NiHCF-HC full cells present a competitive specific energy of over 210 Wh kg-1 and noticeable, long-cyclic performance, as no obvious capacity fading occurs over 1,000 cycles.


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2. EXPERIMENTAL SECTION

Material Synthesis. NiHCF samples were prepared by a co-precipitation route assisted with Na2C2O4 to control the crystallization process. 5 mmol NiCl2 and an appropriate amount of Na2C2O4 were added into 200 mL deionized water, stirring homogeneously to form solution A. Solution B was formed by adding 5 mmol Na4Fe(CN)6‧10H2O, 10 mmol NaCl, and 1.5 g PVP-K30 into 200 mL deionized water. After being dissolved uniformly, a peristaltic pump was used to dropwise added solution A into solution B, continuously for 12 h. After 24 h aging, the precipitated NiHCF particles were filtered and washed several times with ethanol and DI water. Finally, the particles were vacuum dried at 80°C for over 12 h. According to the ratio of Na2C2O4 to NiCl2 (C2O42-: Ni = 0, 1, 2, 3), products were marked as NiHCF-0, NiHCF-1, NiHCF-2, and NiHCF-3, respectively.

Hard carbon (HC) anode was synthesized by the hydrothermal and carbonization route.22 Firstly, appropriate amounts of formaldehyde, resorcinol, and aqueous ammonia were mixed into a beaker under strong stirring for 20 h. Then, a polymer spherical precursor was prepared by a hydrothermal reaction at 100°C for 30 h. The precursor was filtered


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and washed three times with ethanol and DI water, respectively. Subsequently, the sample was vacuum dried at 80°C for 48 h. Finally, HC products were obtained after being carbonized at a processing temperature of 1,200°C for 2 h under N2 atmosphere.

Characterization. In-situ FT-IR characterizations were performed to identify the nucleation and growth process on Fourier-transform infrared instruments (two L160000A FT-IR spectrometers). To characterize the reaction process constantly, a VeeMAX III ATR in-

situ reaction tank was attached to the infrared spectrometer. Solution B, containing Na4Fe(CN)6, was firstly added into the reaction tank, and the initial C≡N band was detected at wavenumbers between 1,800 – 2,300 cm-1. Upon mixing solution A and B in the reaction tank, the FT-IR data was collected continuously for every 20 s in the first minute, and then collected once a minute.

X-ray diffraction with Cu Kα radiation were performed to characterize framework structures (XRD, Panalytical X’pert PRO MRD, Holland). Thermal gravimetric analysis (TGA) data was collected on a Netzsch STA449F3 system from 30 – 800°C under N2 atmosphere. Raman spectra detection were performed using an Ar ion laser with a


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wavelength of 532 nm (LabRAM HR800, Horiba JobinYvon). The chemical composition of NiHCF (Na, Ni, and Fe) was measured by inductively coupled plasma optical emission spectrometry (ICP-OES, ELAN DRC-e, PerkinElmer). The morphology of the as-prepared samples was recorded via SEM (JSM 7600F, JEOL, Japan) and TEM (JEM-2010F microscope, JEOL, Japan) detection.

Electrochemical Measurements. Working electrodes were composed of 5 wt% acetylene black, 15 wt% Ketjen black, 70 wt% active material, and 10 wt% polytetrafluoroethylene (PTFE), which were made into a thin film and rolled onto aluminum meshes, with the areal mass loading of active materials being about 5.5 mgcm-2. Electrochemical tests were carried out in standard CR2032 coin cells. In the half-cells, the counter electrodes were Na metal. In full cells, hard carbon anode consisted of 10 wt% acetylene black, 80 wt% active material, and 10 wt% polyvinylidene difluoride (PVDF) coated onto aluminum foils. To offer a stable charge/discharge platform for the full cells, the mass ratio of anode/cathode were determined to be 1:1. Electrolyte was composed with ethylene carbonate/diethyl carbonate solution (1:1, vol), 2 wt% fluoroethylene carbonate (FEC),


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and 1.0 M NaClO4. All coin cells were assembled in an Ar-filled glovebox. The galvanostatic charge-discharge cycle/rate performance were carried on battery test systems (LAND cycler, Wuhan Kingnuo Electronic Co., China). Cyclic voltammetry (CV) tests were performed from 2.0 to 4.2 V at a scanning rate of 0.1, 0.3, 0.5 and 0.7 mV s-1 on a Princeton electrochemical workstation.

3. RESULTS AND DISCUSSION

All the NiHCF samples were synthesized by the co-precipitation method. Na2C2O4 was used as a chelating agent for controlling synthesis. According to the change of complexation stability constant by the different ratios of C2O42-: Ni, the extent of this control changes. The XRD patterns of the as-prepared samples are shown in Figure 1a, with remarkable peak splitting situated at 24.5° and 50.4° corresponding to the monoclinic phase.23-24 With the increasing amount of C2O42-, the half-width of these peaks became narrower, indicating higher crystal periodicity due to the better synthesis control.25 Also, the weight loss of the first stage around 200°C decreased (Figure 1b), indicating tiny amounts of H2O molecules in the NiHCFs frameworks. With the temperature raised to


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500°C, the NiHCF frameworks were going to collapse.26 The decomposition temperature is higher than reported MnHCFs and CoHCFs,26-27 revealing the as-prepared NiHCFs have stronger bonded framework structure with better thermal stability. Combining the TGA and ICP results, the composition of the NiHCFs is present in Table S1, seen as Na1.16Ni[Fe(CN)6]0.82·1.68H2O

(NiHCF-0),

Na1.27Ni[Fe(CN)6]0.81·2.16H2O

(NiHCF-1),

Na1.66Ni[Fe(CN)6]0.84·2.62H2O (NiHCF-2), and Na2.01Ni[Fe(CN)6]0.85·1.61H2O (NiHCF-3). Without C2O42- serving as a controlling agent, the coprecipitation reaction process occurs simultaneously and rapidly; thus, NiHCF-0 is present with high contents of vacancies and crystal water molecules. With the participation of C2O42-, the competitive reaction between C2O42- and Fe(CN)64- slows down the coprecipitation process, producing highlycrystallized, high-Na content, and low-vacancy NiHCFs. The Rietveld refinements (Figure S1), according to all the XRD profiles, index to a monoclinic lattice with P21/n symmetry.28 The monoclinic frames are varied from a traditional face-centered cubic phase by the accommodation of more Na ions in frameworks (Figure 1c), accompanied by an enlarged skeleton of NiHCF frameworks. In this work, all the samples present high-Na content, with more than 1.1 Na per formula (Table S1), which causes the skeleton variation and results


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in a monoclinic structure,29 and which is caused by the high concentration of Na ions in the precursor solutions. With the 2.01-Na per formula, NiHCF-3 is indexed as a monoclinic structure, as shown in Figure 1d, with lattice constant as a = 10.3025 Å, b = 7.3835 Å, c = 7.3226(4) Å, and β = 91.662°.

Figure 1. (a) XRD patterns and (b) TGA curves of as prepared samples, NiHCF-0 (black), NiHCF-1 (green), NiHCF-2 (blue), and NiHCF-3 (red). (c) PBA framework distortion from


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cubic to monoclinic structure and (d) local structure of monoclinic phased NiHCF-3 stemmed from Rietveld refinements.

Figure 2. (a) SEM, (b) TEM images, and (c) EDS mappings of NiHCF-3 nanoparticles.

The morphology of the as-prepared NiHCF-3 are shown in Figure 2 by SEM and TEM investigation. NiHCF-3 sample is regular cubic shaped, border-rich particles with a clear boundary and smooth surface. The EDS mappings of Na, Ni, Fe, C, and N in Figure 2c show a uniform element distribution. According to the ratio of Na2C2O4 to NiCl2 (C2O42-: Ni = 1, 2, 3), the stability constants of coordination compounds (lgβn) are determined to


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be 5.16, 7.74, and 8.5 at ambient temperatures and pressures.30 Generally, the greater the stability constant is, the stronger the binding of the ligand to the metal ion.31 Mixing NiCl2 and Na2C2O4, Ni2+ ions are preferentially coordinated with C2O42- ions. Then, Ni2+ ions released slowly from the complex, the free Ni2+ ions co-precipitated with hexacyanoferrate groups to form initial nuclei of NiHCFs.12, 14, 16 The stability constant reflects the affinity of chelating agents to metal ions in chelates. With increasing amounts of C2O42-, the chemical species exhibits more efficiency in controlling synthesis. NiHCFs produced without or with smaller amounts of C2O42- manifested as extremely irregular particles that agglomerated together without clear demarcations (Figure S2). Overall, C2O42- is a kind of effective chelating agent in controlling the synthesis of highly crystallized, low-vacancy, and well-dispersed NiHCF particles.

The kinetics of the synthesis process was examined by in-situ infrared spectroscopy using C≡N as a probe group, which only interacts with the coordinate metals at both ends.17 The FT-IR spectra versus time images of the reaction process both without and with C2O42- are shown in Figure 3a and 3b, respectively, with the color gradient indicating the


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intensity of the peak. Looking at the synthesis with C2O42- in Figure 3b, it is apparent that the intensity of the new peak is significantly lower than that in Figure 3a at the same time, indicating a lower rate of coprecipitation reactions. As seen in Figure 3, the blank Na4Fe(CN)6 solution shows a single sharp absorption peak at a wavelength of 2,034 cm-1 belonging to the stretching mode of C≡N coordinating with Fe2+ in free Fe(CN)64- groups.32 After adding Ni2+ ions, an excessive decrease of the ν(CN) peaks at 2,034 cm-1 is observed, and a new, strong peak at 2,088 cm-1 for the ν(CN) mode of Fe-C≡N-Ni emerges. When Fe(CN)64- groups coordinate with Ni2+ ions, covalent bonds formed, N and Ni atoms share electrons, the inner molecular delocalization of N towards Ni, which enhances the C≡N bond strength and shifts the ν(CN) vibrations to higher values.17, 20 The whole reaction process is reflected by the intensity evolution of the stretching frequency of Fe-C≡N-Ni at 2,088 cm-1 (Figure 3d). In the first 20 s, both precipitation solutions go through a burst nucleation process, with C2O42- exhibiting slight effects on this stage. Without controlling with C2O42-, the constantly enhanced relative intensity indicates that there is a new generation of Fe-C≡N-Ni skeletons emerging with


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Figure 3. In-situ infrared spectroscopy during synthesis process (a) without complexing agent controlling, (b) with C2O42- assistant. (c) FT-IR spectra of preparation solution at initial/final state, (d) intensity evolution of FT-IR bands at 2088 cm-1 of Ni-N≡C-Fe. (e) The illustration of coprecipitation process with/without C2O42-.


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prolonged time. The nucleation and crystal growth process are intertwined, which causes irregular-shaped aggregation particles without clear boundaries. With C2O42- control, the relative intensity remained nearly unchanged after the nucleation process, which reveals that nuclei aggregate and merge without the generation of more Fe-C≡N-Ni skeletons throughout the aging process and yields a regularly shaped, highly crystallized, and border-rich NiHCF product, as shown in Figure 3e. As reported, the border-rich morphology is conducive to form passivation layer and lead to an enhanced PBA structure stability during the charge/discharge process.33-34 As an intermediate substance, Na2C2O4 will not affect the final state of the infrared spectrum curve (Figure S3),15 but it does slow down the coordination rate of Ni2+ ions and hexacyanoferrate groups. The in-

situ FT-IR detection provides direct evidence that oxalate is an effective agent for controlling the synthesis of highly-crystallized NiHCF, and it mainly effects the crystal growth process. According to previous reports, the critical stability constants between transition metals and chelating agents are almost in the range of 4 to 9,12, 14, 16 and some


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potential available ligand can be provided, meaning that the mechanism of the controlling can be verified by in-situ FT-IR tests.

The electrochemical performances of the as-prepared NiHCFs are shown in Figure 4. The galvanostatic charge/discharge curves of four samples were measured at the current density of 0.2 C (17 mA g-1). The specific capacities of controlled synthesis NiHCFs (73.3 mAh g-1 for NiHCF-2 and 68.3 mAh g-1 for NiHCF-1) are higher than NiHCF-0 (55.9 mAh g-1). The reduced capacity is due to the loss of activity sites by the emergence of Fe(CN)6 vacancies. In particular, NiHCF-3 exhibits the highest specific capacity of 86.3 mAh g-1, which is close to its theoretical value. Owing to the open framework structure, NiHCF, with large migration channels, provides rapid Na+ ion transition kinetics for high-rate performance. As seen in Figure 4b, NiHCF-3 exhibits great capacity retentions performance as 86.3, 81.4, 79.3, 77.8, 76.1, and 74.9 mAh g-1 at 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C, respectively, and then recovers to 74.8, 76.3, 78.1, 79.3, 80.8, and 85.1 mAh g-1 as the current density shifts back, demonstrating a superior capacity reversibility. While NiHCFs with increasing amounts of water molecules and Fe(CN)6 vacancies are


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present in the frameworks, lattice periodicities are destroyed and migration channels are blocked, leading to a poor rate performance.13 Therefore, it is of great importance to obtain a highly-crystallized NiHCF with low-vacancies. The CV curves of NiHCF-3 at the scanning rate from 0.1 to 0.7 mVs-1 within 2.0 to 4.0 V demonstrate a low polarization. The oxidation/redox peaks at 3.38/3.17 V correspond to the redox reaction of Fe3+/Fe2+, suggesting a superior reversibility and outstanding rate performance. These are also verified by the galvanostatic charge/discharge curves of NiHCF at high rates seen in Figure 4d. It is noticeable that NiHCF-3 shows a remarkable capacity retention of 64.4 mAh g-1 (74.6%) even at 4,250 mA g-1 (50 C), the corresponding galvanostatic chargedischarge curves are shown in Figure S4. The long-term cycle performances are performed at current density of 170 mAg-1. The four NiHCF samples exhibit superior capacity stabilities, with a capacity retention of 90.4%, 86.2%, 84,8%, and 78.0% over 800 cycles (Figure S5) for NiHCF-3, NiHCF-2, NiHCF-1, and NiHCF-0, respectively. The one electron transfer reactions bring hardly any variations for the frameworks and keep the stability of the NiHCF materials in redox reactions,35 which leads to these stable reversible reactions of the four NiHCF samples. While the increasing Fe(CN)6 vacancies


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and water molecules cause the fragile skeletons and side reactions during Na+ insertion/extraction process,36 NiHCF-0, NiHCF-1, and NiHCF-2 exhibit inferior capacity stability compared with NiHCF-3. The excellent electrochemical performance of NiHCF-3 further confirms the high-quality of PBAs cathodes with fewer vacancies, fewer water molecules, and higher crystallinity.


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Figure 4. Electrochemical performances of as-prepared samples. (a) Galvanostatic charge/discharge curves at a current density of 17 mAg-1, (b) rate performance, and (e) cycling performance at 2 C (current density = 170 mA g-1). NiHCF-0 (black), NiHCF-1


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(green), NiHCF-2 (blue), and NiHCF-3 (red), respectively. (c) CV curves and (d) galvanostatic charge/discharge curves of NiHCF-3 at different rates.

For practical applications, the NiHCF/hard-carbon full cells were fabricated, shown in Figure 5. Before the full-cells assembly, a Na insertion process was necessary for the preparation of hard-carbon anode.28 The charge/discharge curve for the NiHCF-3 shows the plateau of Fe2+/Fe3+ at 3.3 V; the hard carbon/Na half-cell shows a voltage platform when the voltage is lower than 0.1 V (Figure 5a). The specific capacity of HC is about 325 mAh g-1, which is significantly higher than the cathode material (~85 mAg-1). To offer a stable charge/discharge platform for the full cells, the hard-carbon anode was set at a certain capacity excess to the NiHCF cathode, and only the platform part of the hardcarbon served in redox reactions. The galvanostatic charge/discharge curves of the full cells at different current density are shown in Figure 5b. The full cell shows superior electrochemical behavior with a discharge capacity of 78.1 mAh g-1 at 0.2 C (based on the mass of active material) and a maintaining capacity of 73.2 mAh g-1 at 2 C


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corresponds to the capacity retention as high as 93.7% with a high Na+ insertion platform at ~3.1 V and great rate performance. The excellent long-term cycle performance of the full cell is shown in Figure 5c, with an extremely high capacity retention of 95.2% over 1,000 cycles, and the coulombic efficiency approaching 100% in the whole cyclic process. With the high reaction voltage, the specific energy is calculated as 210.5 Wh kg-1 for such fabricated NiHCF//HC full cells, shown in Figure S7. Although there is no obvious capacity attenuation, the specific energy decreased. As seen the inset charge/discharge curves in Figure S7c, the Na+ insertion reaction specific capacity remained at 69.7 at the 1,000th cycle from 73.2 mAh g-1 at the initial time. The reaction voltage decreased from 3.2 V to 2.8 V. With the ultra-stability of NiHCF cathodes, the voltage decrease is owed to the enhanced potential (VS. Na+/Na) of hard carbon anode by the consumption of Na+ ions in cyclic reactions.37 The as-assembled full cells exhibit a specific energy retention of 166.9 Wh kg-1 (79.3%) at the 1,000th cycle. Compared with previous reports (Figure 6),16, 38-44

NiHCF-HC full cells in this work present a competitive specific energy and noticeable,

long-cyclic performance, which is essential for practical application.


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Figure 5. Full-cell (NiHCF-3/HC) electrochemical performances with mass ratio of anode/cathode equal to 1. (a) Voltage profiles of NiHCF-3 cathode and hard carbon anode, (b) galvanostatic charge/discharge curves at different rates, and (c) long-term cycle performance at current density of 170 mA g-1 (calculated by cathode active mass).


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Figure 6. Specific energy and cyclic performance in this work compared to previously reported PBAs cathode full cells (calculated by cathode active mass). 16, 28, 38-44

4. CONCLUSION

The ultra-stable NiHCF-3 cathode with low content of Fe(CN)64- vacancies and water molecules, and high content of Na+ ions are synthesized by a facile oxalate-controlled method. Via in-situ infrared spectroscopy detection, it was verified that the addition of the C2O4-2 chelating agent can effectively control the synthetic kinetics. The competitive reaction between C2O42- and Fe(CN)64- slightly slows down the nucleation process and mainly inhibits the new generation of Fe-C≡N-Ni skeletons during the aging process. Benefitting from high crystallinity and few [Fe(CN)6] defects, the NiHCF-3 exhibits a good reversible capacity of 86.3 mAh g-1, excellent rate capability with a remarkable capacity


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retention of 64.4 mAh g-1 (74.6%) at 50 C, and a superior long-term cycling ability of 90% capacity retention over 800 cycles at the current density of 170 mAg-1. Moreover, the full cells were fabricated with NiHCF-3 cathode and hard-carbon anode, which delivered a capacity of 75 mAh g-1 without noticeable capacity decay, even over 1,000 cycles. The

in-situ infrared-spectroscopy-assisted synthetization can be developed to explore effective chelating ligands for high-performance PBAs cathode materials applied in largescale energy storage systems.

ASSOCIATED CONTENT

Supporting Information.

The Supporting Information is available free of charge via the internet http://pubs.acs.org. The following files are available free of charge. XRD patterns, SEM images and additional electrochemical data. (PDF)


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AUTHOR INFORMATION

Corresponding Authors *E-mail: [email protected]

*E-mail: [email protected]

ORCID Jiantao Han: 0000-0002-9509-3785

Author Contributions †Yue

Xu and Miao Chang contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

The financial support from the National Key Research and Development Project of China (Grant Nos. 2016YFB0700600 and 2016YFB010030X), and the National Natural Science Foundation of China (Grant Nos. 51632001, 51732005, 51702111, and 51772117). And


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we thank the State Key Laboratory of Materials Processing and the Die & Mould Technology of HUST Analytical and Testing Centre of HUST and for SEM, TEM, TGA, XRD, Raman, and other measurements.

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TABLE OF CONTENTS

An in-situ FT-IR assisted synthesis was performed to obtained high performance nickel hexacyanoferrate cathodes for long-life sodium-ion batteries.


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In Situ FTIR-Assisted Synthesis of Nickel Hexacyanoferrate Cathodes

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