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A Quasi-Solid-State Sodium-Ion Full Battery with High-Power/Energy Densities Jin-Zhi Guo, Ai-Bo Yang, Zhen-Yi Gu, Xing-Long Wu, Wei-Lin Pang, Qiu-Li Ning, Wen-Hao Li, Jing-Ping Zhang, and Zhong-Min Su ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b02768 • Publication Date (Web): 02 May 2018 Downloaded from http://pubs.acs.org on May 2, 2018

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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ACS Applied Materials & Interfaces

A Quasi-Solid-State Sodium-ion Full Battery with High-Power/Energy Densities †

†

†‡

†

†

†

Jin-Zhi Guo, Ai-Bo Yang, Zhen-Yi Gu, Xing-Long Wu,* § Wei-Lin Pang, Qiu-Li Ning, WenHao Li,† Jing-Ping Zhang,† Zhong-Min Su*† †

National & Local United Engineering Laboratory for Power Batteries, Faculty of Chemistry,

Northeast Normal University, Changchun, Jilin 130024, P. R. China ‡

College of Chemistry and Environmental Science, YiLi Normal University, Yining, Xinjiang

835000, P. R. China §

Institute of Advanced Electrochemical Energy, Xi'an University of Technology, Xi'an 710048,

P. R. China. Corresponding Author * E-mail: [email protected] * E-mail: [email protected]

KEYWORDS: Sodium-ion full battery; quasi-solid-state; gel-polymer electrolyte; high energy and power densities; Na3V2(PO4)2O2F cathode

1 Environment ACS Paragon Plus

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Developing high performance, low-cost and safer rechargeable battery is a primary challenge to the next-generation electrochemical energy storage. In this work, a quasisolid-state (QSS) sodium-ion full battery (SIFB) is designed and fabricated. Hard carbon cloth derived from cotton cloth and Na3V2(PO4)2O2F (NVPOF) is employed as anode and cathode, respectively, and a sodium ion conducting gel-polymer membrane is used as both QSS electrolyte and separator, accomplishing the high energy and power densities in the QSS sodium ion batteries. The energy density can reach 460 W h kg−1 according to the mass of cathode materials. Moreover, the fabricated QSS SIFB also exhibits the excellent rate performance (e.g., about 78.1 mA h g−1 specific capacity at 10 C) and superior cycle performance (e.g., ~ 90 % capacity retention after 500 cycles at 10 C). These results show that the developed QSS SIFB is a hopeful candidate for the large-scale energy storage.

1. INTRODUCTION On account of the finite nature of fossil fuels and rising concerns about environmental pollution, studies on storage for clean and renewable energy are more important than ever before. The efficient energy storage technology is an important component in exploitation of sustainable energy resources. The large-scale energy storage systems (ESSs) on the basis of secondary batteries have drawn much attention for their high energy conversion efficiency, adjustable power, long cycle life and low cost.1, 2 Although lithium-ion batteries (LIBs) have been rapidly developed and extensively applied, the low abundance lithium resources in the Earth’s Crust cannot satisfy substantial demand for upcoming larger-scale ESSs.3-6 Thus, it is greatly necessary to develop new inexpensive and efficient ESSs.7


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Sodium-ion batteries (SIBs) are hopeful options, because of identical working principle as LIBs, highly abundant resources and widespread geological distribution of sodium.8-12 During past years, numerous trials have been devoted to developing suitable electrode materials for SIBs. Recently, the reliability and practicability of sodium-ion full batteries (SIFBs) have been paid much attention, and great efforts have also been dedicated to evaluating the SIFBs, including

Fe3O4//Na2FeP2O7,13

Sb//Na3V2(PO4)3,14,

15

Na3V2(PO4)3

symmetric,16,

17

Sb//Na3V2(PO4)2O2F,18 Na2Ti3O7//VOPO4,19 hard carbon//NaNi0.5Mn0.5O220 and so on. However, these full cells are still confronted with several challenges, such as low-operating voltage, inferior rate capability, short-term cycle life, and low-power/energy densities. In order to construct the advanced SIFBs with high working voltage and high energy density, the choice of superior cathode material should be the most vital, because the practicable anode is very limited and almost fixed as carbon materials. Carbonaceous materials have been generally studied as negative electrode materials for SIBs by reason of numerous edge/defective sites and large layer spacing for Na+ insertion/extraction, especially the hard carbon with the reversible capacity of about 300 mA h g-1 and low operating potential (almost zero versus Na+/Na) and have been testified to markedly enhance the electrochemical performance of SIBs.21,

22

Among all the

cathode materials for SIBs, fluorophosphates Na3V2(PO4)2O2F (NVPOF) with the crystal structure of a Na-super-ionic conductor (NASICON) should be the most promising cathode candidate for SIFBs because of their stable 3D crystalline structure, high discharge plateaux at about 4.01 and 3.60 V versus Na+/Na and good thermal stability.18, 23, 24 In spite of its merit of low price, the security issues confronted for LIBs also exist in SIBs because of the utilization of easily leaked and flammable organic liquid electrolytes, especially in large-scale ESSs.25, 26 The polymer electrolytes, usually divided into solid and gel electrolyte,



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should be the most promising candidates of electrolytes for safe and flexible rechargeable batteries.27-29 The solid-polymer electrolytes have been vastly explored because of their higher security compared with the gel-polymer electrolytes (GPE).30,

31

However, they are still

confronted with several challenges at the present stage, containing low ionic conductivity at ambient temperature and poor contact/interfacial properties (high interfacial resistance, poor/unstable contact with electrodes).32,

33

Nevertheless, the GPE, which possess the hybrid

characteristics combining polymer with liquid electrolytes, have attracted extensive attention due to higher ionic conductivity, broad electrochemical window, good thermodynamic stability, and a higher electrolyte uptake than conventional separators.34-36 Hence, an efficient and compromised method to solve the safety issues is achieving quasi-solid-state (QSS, i.e. gel state, an intermediate state between liquid state and all solid state) storage devices using QSS electrolytes. Herein, we design a novel QSS SIFB based on a cotton cloth derived from hard carbon cloth (CC) as binder-free anode and Na3V2(PO4)2O2F (NVPOF) that we recently reported as cathode.18 A sodium ion conducting gel polymer based on poly(vinylidenefluoride-cohexafluoropropylene) (P(VDF-HFP)) membrane can serve as both electrolyte and separator. For convenience, the as-fabricated QSS SIFBs are written as “CC//NVPOF” below. The designed CC//NVPOF exhibited the promising electrochemical characteristics, such as a high energy density of ~ 460 W h kg−1 (calculated from the mass of cathode materials) with a high average operating voltage of about 3.80 V, superior rate capability and excellent cycling performance. Obviously, a superior electrochemical performance is demonstrated in the P(VDF-HFP) GPE because of the super-fast ion transport within NVPOF, which was disclosed by the galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV) studies. The unique battery


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system pushes the power/energy densities of SIBs to a high level, and is a hopeful candidate for large-scale energy storage applications.

2. EXPERIMENTAL SECTION Preparation of sodium ion conducting gel polymer electrolyte The P(VDF-HFP) membrane is based on literature reported with minor modifications.37 Typically, P(VDF-HFP) was added into a solution which contains N,N-dimethyl formamide (DMF) and distilled water with a ratio of 17:1 by weight percent. After treated in a water bath at 80 °C, a watch-glass was employed to be the next holder for the solution by providing a smooth surface for the spreading of the solution. And then, the watch-glass was immersed in a water with a constant temperature at 80 °C, resulting the successful formation of homogeneous white membrane. After dried in vacuum oven at 100 °C, the dried membrane was cut in to circular pieces with a diameter of 15 mm. Finally, after soaking in an organic electrolyte (1 mol L-1 NaClO4 solution consist with propylene carbonate and fluorinated ethylene carbonate at a ratio of 95:5 in volume as an electrolyte additive) over 12 h in a glove box, the gel polymer electrolyte (GPE) was successfully prepared for further electrochemical measurement. Preparation of the Na3V2(PO4)2O2F material (NVPOF) The NVPOF cathode material was prepared according to our recent reports.18 Preparation of the CC anode derived from cotton cloth



In order to prepare the CC anode, a commercially available cotton cloth was calcined at 1200 °C for 2 hours under Ar atmosphere. The CC anode was washed in hydrochloric acid solution and distilled water several times and dried at 80 °C. Material characterizations XRD test was used to analyse the crystal texture and purity of the sample in the 2θ range of 10-80°. The microscopic morphology and structure were studied by using scanning electron microscopy (SEM, Hitachi SU8000). Thermogravimetric analysis (TGA, Pyris Diamond TG/DTA, PerkinElmer) was carried out under N2 atmosphere at a temperature range of 30 to 300 °C with a heating rate of 5 °C min-1. Electrochemical measurements The counter/reference electrode and electrolyte in the CR2032 coin-type half cell were made of Na metal and P(VDF-HFP) GPE, respectively. The NVPOF electrode was consist with active material, acetylene and carboxymethylcellulose dissolving in deionized water and covering on aluminium foil at a ratio of 7:2:1 in weight percent. And then, the electrode was dried in vacuum oven at 60 °C over night. The loading density of active material on the electrodes is about 2.0-2.5 mg cm-2. The prepared CC was directly used as binder-free work electrode. GCD tests were carried out on the LAND CT2001A in a potential range of 3.0-4.3 V and 0.01-2 V for half cells. A CV test of varied scan rates from 0.03 to 0.1 mV s-1 was employed on a VersaSTAT 3 (Princeton Applied Research) electrochemical station. A GITT analyse was used in which the cells were charge/discharge in the potential window of 3.0-4.3 V vs. Na+/Na at a rate of 0.04 C. And there were 1 hour’ applied galvanostatic current and 6 hours’ rest for the duration time, respectively. Full cells were assembled by matching capacity of NVPOF cathode


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with CC anode in excess of 5-10 % of anode capacity. The mass of cathode material was used to calculate the specific capacities of full cells. A pre-sodiation for CC anode was employed to active the material and stabilize the electrode surface before the assembling of CC//NVPOF full cells.

3. RESULTS AND DISCUSSION The P(VDF-HFP) polymer membrane was synthesized via a simple method that described previously.37 Figure 1 displays the composition and morphology of P(VDF-HFP) membrane by powder X-ray diffraction (XRD) test, optical photos and scanning electron microscopy (SEM). Figure 1a shows the XRD pattern of porous P(VDF-HFP) membrane, obviously, there are two intense peaks at 18.14ºand 19.64º which is consistent with the literature reports.38 Figure 1b reveals the optical photographs of the P(VDF-HFP) membrane (top) and its GPE (bottom). A transparent GPE was obtained after the soaking in the liquid electrolyte, demonstrating the liquid electrolyte was resoundingly absorbed into the pores of the P(VDF-HFP) substrate. Figure 1c and 1d show the SEM images of the surface morphology of P(VDF-HFP) membrane. On the surface of the membrane, there are abundant pores (d = 1−2 µm) that is advantageous for absorbing and retaining the liquid electrolyte. The average thickness of the membrane is measured by micrometer caliper and is found to be around 170 µm. The porosity of the membrane is found to be around 68%. Its liquid electrolyte uptake is up to 203 %, and the membrane demonstrated the good retainability for the liquid electrolyte compared with the common separator of glass filter, the more detailed data are shown in Figure S1 and Table S1. Such a high liquid electrolyte uptake is because of the high porosity of the P(VDF-HFP) substrate. Although we prepare the P(VDF-HFP) membrane based on the literature report,37 we optimized the synthesis conditions



and the as-prepared P(VDF-HFP) membrane with the best characterizations. Besides, we also measure the ionic conductivity of the GEP by the electrochemical impedance spectroscopy method, as shown in Figure S2. The ionic conductivity of P(VDF-HFP) GPE is about 0.42 mS cm−1 at room temperature. Furthermore, the thermal stability of P(VDF-HFP) GPE have been measured by TGA tests. As shown in Figure S3, P(VDF-HFP) GPE exhibits the best thermal stability compared with the glass fiber membrane and commercial separator (NW1640) containing the same amount of electrolyte as P(VDF-HFP) GPE. That is, the evaporation rate of organic electrolyte in P(VDF-HFP) GPE is slowest, demonstrating much enhanced retainability for liquid electrolyte in P(VDF-HFP) GPE than the common separators. The NVPOF cathode material was prepared via a controlled hydrothermal method as recently reported by us.18 Shown in Figure S4a is the XRD pattern of the NVPOF cathode material, indicating that all the characteristic peaks of material can be well indexed to the NASICON-type Na3V2(PO4)2O2F of I4/mmm space group. The SEM images in Figure S4b displays that the length and width of NVPOF material is about 400 and 200 nm, respectively. This well coincides with our previous studies.16 Figure S5 is the XRD pattern and SEM image of the CC anode. As disclosed, the XRD pattern exhibits broad peaks at 20° and 43°, which corresponds to the lattice planes of (002) and (100) in the disordered carbon. As shown in Figure S5b, the CC anode is composed of interwoven mesh of hollow microtubules and the diameter of hollow microtubule is around 10−15 µm, which coincides well with our previously reported.39 Electrochemical performance of the NVPOF cathode is firstly evaluated by galvanostatic charging/discharging (GCD) tests in half cells with the P(VDF-HFP) GPE as both electrolyte and separator. Figure 2a shows the outstanding rate capabilities of NVPOF with capacity of 125.5 mA h g−1 at 0.1C, and the corresponding initial Coulombic efficiency is ~ 90.35 %. This value is


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very close to 127.8 mA h g−1 in liquid electrolyte recently reported by us,16 suggesting the high ionic conductivity of the P(VDF-HFP) GPE. Even at 10 C, it still delivers a capacity of ~ 84 mA h g−1. This value equates to a capacity retention of ~ 72% compared to the specific capacity at 0.1 C, indicating that only 28% of the specific capacity is cut back even though the rate augments 100 times. The GCD curves at different rates (inset of Figure 2a) disclose a clear charge/discharge plateau even at 10 C. We also analyzes the polarization phenomenon in the whole range of rates. As shown in Figure S6, the NVPOF cathode reveals the minor polarization even at 10 C. The NVPOF cathode also exhibits outstanding cycling performance at different rates of 0.2 and 1 C. After 200 cycles at a relatively low rate of 0.2 C (Figure 2b), the NVPOF achieves a capacity retention of above 95% with the capacity decay from the initial 118.9 to 113.1 mA h g−1. Figure 2c gives its cycling performance at 1C, as shown, the capacity retention is still up to 94.6 % after 1500 cycles, implying the superior cycling stability of the NVPOF electrode in the P(VDF-HFP) GPE. This finding is also verified by the crystal structure and morphology tests after cycling (Figure S7). The capacity fading rates per cycle was only 0.0036% at 1 C. Notably, the above data are superior to the previous reports that studied in the liquid electrolyte by us.18 To analyze the reaction kinetics of NVPOF electrode during Na+ de-/intercalation processes in the P(VDF-HFP) GPE, CV and GITT tests were employed in the NVPOF half cells. In Figure 3a, CV curves were recorded in the voltage window of 3.0-4.3 V versus Na+/Na at various scanning rates from 0.1 to 1.0 mV s−1. With the increse of scanning rate, the peak currents also increase continuously, at the same time the cathodic or anodic peaks shift to lower or higher potentials. Figure 3b shows linear fitting profiles between the peak current densities (ip) and square root of scanning rates (v1/2). The excellent fitting results and high R values imply that the



electrochemical

Na-intercalation/extraction

reactions

are diffusion-controlled

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processes.

Consequently, the apparent Na-diffusion coefficient (Dapp,Na) can be counted according to the Randles–Sevcik equation (1):40 ip = 2.69 × 105n3/2ADapp,Na1/2C0 v1/2

(1)

where ip is peak current of cathodic or anodic peaks, n is the number of electrons per molecule during the Na+ intercalation (n = 2 for V4+/V5+ redox pair), A is the surface area for the electrode, C0 is the concentration of Na+ in the electrode (0.0077 mol cm-3),41 and v is the scanning rate. The Dapp,Na values are 6.50 × 10−13, 6.84 × 10−13, 8.51 × 10−13, and 9.74 × 10−13 cm2 s−1 for peaks A1, C1, A2, and C2, respectively. Evidently, the low-potential A1/C1 redox couple yields smaller Dapp,Na values than those of the high-potential couple, suggesting that Na intercalation/extraction at a low potential of around 3.5 V is relatively sluggish and requires higher energy. which is acommon result and consistent with previous reports in liquild electrolyte.18 GITT was measured at 0.04 C over the potential window of 3.0−4.3 V vs. Na+/Na in 1st cycle. Figure S8 shows the applied current flux and resulting voltage profile for a single titration during the 1st charging and discharging process of NVPOF electrode in P(VDF-HFP) GPE. A straight-line behavior is observed between the cell voltage E and the square root of galvanostatic time τ1/2, as shown in the inset of Figure S8a and S8b, from which Dapp,Na values can be counted according to the following equation (2):42

, =

∆

∆ ≪ /

(2)


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where mB, MB, and VM is the mass, molecular weight, and molar volume of the NVPOF, respectively; τ is the time for an applied galvanostatic current; S is the surface area of electrode; L is the average radius of the material particles; and ∆Es and ∆Eτ are the quasi-equilibrium potential and the change of cell voltage E during the current pulse, respectively. The evolution of quasi-equilibrium potential and calculated Dapp,Na values along with the GCD curves are shown in Figure 3c. Notably, each quasi-equilibrium potential (the red squares in Figure 3c) is extremely close to the GCD curves, indicating the Na intercalation/extraction processes are kinetically fast with high ionic and electronic. Form the GITT tests, the values of Dapp,Na are in the 10−11~10−12 cm2 s−1 order of magnitude, and a similar tendency is observed at both charging and discharging processes. Compared the results of CV, the values of Dapp,Na obtained from GITT are higher, because the actually measured value of ∆Es in GITT is large. Another reason could be the thermodynamic factor, which gives rise to the deviation from ideal crystallized material.37 As is well-known that the strain and surface energy can make for the formation energy of the real material, which can affect the open circuit voltage and may give rise to a varied ∆Es value during the entire charging/discharging processes.43 Furthermore, the Dapp,Na values at the upper plateau are obviously larger than those at the lower plateau, indicating that Na intercalation/extraction is relatively sluggish and requires higher energy at a low potential of around 3.60 V, and in the middle of each plateau the values are clearly smaller than those at the both ends, which is a common result and consistent with previous reports in liquid electrolyte16 and other electrode materials.40, 44 As discussed above, the P(VDF-HFP) GPE should be a promising electrolyte with the high ionic conductivity. Hence, a QSS SIFB using the prepared NVPOF as cathode, CC as flexible and self-supporting anode (Figure S5 and S9) and P(VDF-HFP) GPE as both electrolyte and



separator was assembled and studied. Meanwhile, we also evaluate the performance of CC anode in P(VDF-HFP) GPE, as shown in Figure S9. The CC anode exhibits the superior cycling stability with a capacity retention of more than 85% after 100 cycles at 0.5 C (corresponding current density of 65 mA g-1), and the Coulombic efficiency is ~ 77.29 %. A schematic illustration of the assembled QSS SIFB is displayed in inset of Figure 4a. The typical GCD curves of the NVPOF cathode and CC anode were performed at 0.1 C in half cell, as shown in the Figure 4a. Evidently, there are excellent two pairs of oxidation/reduction plateaux at 4.03/4.02 and 3.63/3.62 V vs. Na+/Na in NVPOF cathode whereas the average discharge/charge plateau of CC anode is about 0.06/0.08 V vs. Na+/Na. On basis of the GCD tests, it can be rationally deduced that, the average voltage output of the assembled CC//NVPOF full cells will be about 3.80 V as already testified by GCD curves (Figure 4b). In the GCD curves, the discharge capacity is about 121.0 mA h g−1 at 0.1 C with an initial Coulombic efficiency of 93.66%. As a result, the energy density delivered by the CC//NVPOF is ~ 460 W h kg−1 calculated on the mass of the NVPOF cathode. Therefore, energy density of the finally commercialized CC//NVPOF can reach ~ 184 W h kg−1 if the mass percentage of cathode material is about 40 % in the whole battery. Figure 4c is the representative CV profiles tested at 0.1 mV s−1. Obviously, there are two couples of anodic/cathodic peaks at 4.03/3.94 V and 3.62/3.50 V, and the average working voltage is ~ 3.80 V in discharging processes, which is well identical to the predicted value in Figure 4b. To further evaluate the electrochemical performance of the assembled CC//NVPOF full cells, the rate and cycling performances were investigated by GCD tests at various rates. Shown in Figure 5a, the rate capability was obtained from 0.1 to 10 C, exhibiting an outstanding highrate performance. Even at 10 C, the delivered discharge capacity is still 78.1 mA h g−1 with a


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capacity retention of ~ 65% compared to specific capacity at 0.1 C. The corresponding GCD curves of CC//NVPOF at different rate are further exhibited in Figure 5b, there are still two clear discharge plateaux of about 3.75 and 3.2 V at 10 C. Furthermore, the specific capacity at 0.1 C can well restore to its initial values after the rate tests of 45 cycles, implying that the CC//NVPOF full cells can work at arbitrarily varied current densities. This outcome promotes the capability of CC//NVPOF full cells to store unstable and intermittent energy sources, for instance, wind and solar energies. More importantly, the CC//NVPOF full cells also exhibit outstanding cycling performance, as shown in Figure 5c. When cycled at 1 C, the CC//NVPOF full cell delivers an initial capacity of 116.1 mA h g−1 with a capacity retention of about 92.2 % after 200 cycles. To test the much longer cycle life, the CC//NVPOF full cell was further cycled at 10 C, exhibiting a capacity retention of about 90 % even after 500 cycles. In addition, we summarized and compared many recently reported QSS full-cell configurations based on the SIBs and LIBs in regard to their energy and power densities, as presented in Figure 6. As seen in the Ragone plots, the CC//NVPOF possesses a high energy density of almost 460 W h kg−1 at a power density of 52 W kg−1, which is notably higher than those

of

the

majority

of

reported

ones

except

for

the

lithium

based

oxides

graphite//Li(Ni1/3Co1/3Mn1/3)O2.45 Although the energy densities of the CC//NVPOF are slightly lower than those of graphite//Li(Ni1/3Co1/3Mn1/3)O2 at power density of < 300 W kg−1, it exhibits markedly superior power performance. Moreover, the power/energy densities of the CC//NVPOF are notably higher than the Sb//Na3V2(PO4)3.14 By comparison, our CC//NVPOF reveal the outstanding electrochemical performances, and more details are displayed in Table S2.

4. CONCLUSIONS



In summary, a QSS SIFB CC//NVPOF has been fabricated based on the CC as binder-free anode and NVPOF as cathode, using a P(VDF-HFP) GPE as both electrolyte and separator. Such a full cell can exhibit a high energy density of ~ 460 W h kg−1 (calculated based on the mass of the NVPOF) with a high average operating voltage of above 3.80 V. Electrochemical tests demonstrate that the assembled CC//NVPOF exhibits the outstanding electrochemical performance in the aspect of excellent rate capability and ultralong cycling stability, illustrating the designed CC//NVPOF would be a hopeful candidate for advanced secondary batteries with high-power/energy densities. More importantly, the GITT and CV tests were implemented to analyze the Na-migration kinetics of the NVPOF electrode in the P(VDF-HFP) GPE during the Na+ de-/intercalation processes.


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b (021)

(110)

(020)

a Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10

20

30

P(VDF-HFP) membrane

40

50

60

70

80

Gel polymer electrolyte

2 Theta (deg.)

c

d

3 µm

500 nm

Figure 1. Structural and morphology characterizations of the P(VDF-HFP) polymer membrane. (a) XRD pattern, (b) optical photograph, (c) and (d) SEM images.



120

80

40

Unit: C 1

2

3

5

8

10

4.5 4.0

charge discharge

3.5

0.1 C

10 C

3.0 0

30

60

90

120

Specific Capacity (mA h g-1)

0 0

10

20

30

40

160 120 80 40 0


4.5 4.0 3.5

1st 5th 10th

3.0 0

30

50th 100th 200th

60

90

120


-40

50

0

Cycle Number (n)

c

charge discharge

0.2 C Potential (V vs. Na+/Na)

0.1 0.2 0.5


b

160

Potential (V vs. Na+/Na)


a

50

100

150

Cycle Number (n)

200

120

160

100 80

120 60 1C

80

40

40

20 0

0 0

300

200

600

900

1200

Coulombic efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1500

Cycle Number (n)

Figure 2. Electrochemical performance of the NVPOF cathode in half cells. (a) Rate capability and the corresponding GCD curves (inset). (b) The cycling performances and the corresponding GCD curves (inset) at 0.2 C. (c) The long cycling stability with Coulombic efficiency over 1500 cycles at 1 C.


Current Density (A g-1)

a

0.10 A1

0.03 mV s-1 0.04 mV s-1

0.05

0.05 mV s-1 0.07 mV s-1 0.1 mV s-1

0

-0.05 C1

C2

-0.10 3.0


c

b8

A2

3.3

3.6

3.9

4 A1 A2 C1

0

C2

-4

-8 4.2

4.5

5

6

7

8

9

10

-1

v 1/2 (x10-3V s )1/2

Potential (V vs. Na+/Na) 4.5

1E-9 4.0 1E-10 3.5 1E-11

3.0

Dapp,Na (cm2 s-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Peak Current (X10 -5 A)

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1E-12

2.5 0

30

60

90

120

0

30

60

90

120


Figure 3. Studies of Na-migration kinetics for the NVPOF electrode in the P(VDF-HFP) GPE. a) CV profiles at various scan rates from 0.03 to 0.1 mV s−1. b) Linear fitting for the relationship between ip and v1/2 from CV profiles. c) GITT test results showing the changes of Dapp,Na and quasiequilibrium potentials along with the GCD processes.



a

0

0.2

0.4

0.6

0.8

1.0

4.5

b

4.5 0.1 C

Voltage (V)

0.1 C 4.0

3.5 NVPOF cathode

4.0

3.5 1st 2nd 3rd

-

e

Power Supply

3.0

3.0

e-

2.5

-

+

0

30

60

90

120


2.0

c 0.2

1.5 Cathode


Current Density (A g-1)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 27

Anode

CC anode

1.0 0.5 0 0

0.2

0.4

0.6

0.8

1.0

0.1

0.1 mV s-1

0 1st 2nd 3rd

-0.1 -0.2 2.5

Normalized Capacity

3.0

3.5

4.0

Voltage (V)

Figure 4. (a) The GCD curves of both CC and NVPOF electrodes at 0.1 C in half cells; inset is the schematic illustration of CC//NVPOF full cells. The performance of the CC//NVPOF full cells: (b) GCD curves at 0.1 C and (c) CV patterns of initial three cycles.


Page 19 of 27

b

160 0.1 0.2 0.5

120

4.5

Unit: C 1

2

3

Voltage (V)


a

5 8 10

80

4.0

3.5

charge discharge

40

3.0

0

10

20

30

40

50

0

Cycle Number (n)

30

60

90

120 -1

Specific Capacity (mA h g ) 120

200

-1

Specific Capacity (mA h g )

c

0.1 C

10 C

0

100

160

80

1C

120

60

10 C 80

40 40

20

0

Coulombic efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0 0

100

200

300

400

500

Cycle Number (n)

Figure 5. Electrochemical performance of the CC//NVPOF full cells. Rate capability (a) and the corresponding GCD curves (b). (c) The cycle stabilities at different rates of 1 C for 200 cycles and 10 C for 500 cycles.



600 graphite//Li(Ni1/3Co1/3Mn1/3)O2

Energy Density (W h kg-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 27

500 400

300

200

This work graphite//LiFePO4 Sn-C//LiMn0.5Fe0.5PO4

Sb//Na3V2(PO4)3

100

1000

10000

Power Density (W kg-1) Figure 6. Ragone plots for the CC//NVPOF full cells compared with other literature works on QSS full cells. 11, 45-47

ASSOCIATED CONTENT Supporting Information. Characterizations for P(VDF-HFP) GPE; XRD patterns and SEM images for NVPOF cathode and CC anode; single GITT profile for NVPOF cathode; electrochemical performance for the CC anode; comparison of electrochemical properties. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]


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* E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (51602048), and the Fundamental Research Funds for the Central Universities (2412017FZ013).

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e-

600

Power Supply

e-

+

-

Energy Density (W h kg-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


500

This work

400

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Cathode


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Anode

1000

Power Density (W kg-1)


Energy

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