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Poly-#-glutamate Binder to Enhance Electrode Performances of P2-Na2/3Ni1/3Mn2/3O2 for Na-ion Batteries Yusuke Yoda, Kei Kubota, Hayata Isozumi, Tatsuo Horiba, and Shinichi Komaba ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01362 • Publication Date (Web): 06 Mar 2018 Downloaded from http://pubs.acs.org on March 7, 2018
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Poly-ɤ-glutamate Binder to Enhance Electrode Performances of P2-Na2/3Ni1/3Mn2/3O2 for Na-ion Batteries Yusuke Yodaa, Kei Kubotaa,b, Hayata Isozumia, Tatsuo Horibaa,b, and Shinichi Komaba*a,b a
Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan.
b
Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, Nishikyoku, Kyoto 615-8245, Japan
KEYWORDS: sodium ion batteries, layered materials, Na2/3Ni1/3Mn2/3O2, water-soluble binder, Poly-ɤ-glutamate. ABSTRACT: P2-Na2/3Ni1/3Mn2/3O2 (P2-NiMn) is one of the promising positive electrode materials for high-energy Na-ion batteries because of large reversible capacity and high working voltage. Although by charging up to 4.5 V vs. Na+/Na, the capacity rapidly decays during charge/discharge cycles, which is caused by the large volume shrinkage of 23.2% by sodium deintercalation and following electric isolation of P2-NiMn particles in the composite electrode. Serious electrolyte decomposition at the higher voltage region than 4.1 V brings deterioration of the particle surface and capacity decay during cycles. To solve these drawbacks, we apply water-soluble sodium poly-ɤ-glutamate (PGluNa) as an efficient binder to P2-NiMn instead of conventional poly(vinylidene difluoride) (PVdF) and examined the electrode performances of P2-NiMn composite electrode with PGluNa binder for the first time. The PGluNa electrode shows Coulombic efficiency of 95% at the 1st cycle and capacity retention of 89% after 50 cycles, while the PVdF electrode exhibits only 80% and 71%, respectively. AC impedance measurements reveal that the PGluNa electrode shows much lower resistance during cycles compared with the 1 ACS Paragon Plus Environment
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PVdF one. From surface analysis and peeling test of the electrodes, the PGluNa binder covers surface of the P2-NiMn particles and suppresses electrolyte decomposition and surface degradation. The PGluNa binder further enhances mechanical strength of the electrodes and suppresses electrical isolation of the P2-NiMn particles during sodium extraction. The efficient binder with noticeable adhesion strength and surface coverage of active materials and carbon has paved a new way to enhance electrochemical performances of high-voltage positive electrode materials for Na-ion batteries.
1. INTRODUCTION Since lithium ion batteries were commercialized in 1991, the market of the batteries has been expanding rapidly and demands for them become diversified from electronic devices to electrified vehicles or stationary power storage systems. Such rapid expansion of the market naturally brings us anxiety about depletion and production restraint of natural resources. Therefore, environment-friendly batteries to contribute to sustainable society are recently focused, so that, research and development of rechargeable batteries without costly or toxic elements such as Li, Co, and Pb are attracting our attention.1 Sodium ion battery is one of the promising innovative batteries among many choices of proposed new batteries, because sodium is an abundant element and the resources are low-cost, which is preferable to large-scale application.2 As for a positive electrode material for the battery, our group has reported P2-NaxFe1/2Mn1/2O2 made from only abundant elements, which is very favorable in terms of practical perspective.3
P2-
NaxFe1/2Mn1/2O2 shows a high discharge capacity of 190 mAh g-1 in a voltage range of 1.5
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– 4.3 V to achieve high energy density comparable with lithium ion battery materials. However, its poor cyclability still remains to be a serious issue, for long-term cycling stability is required along with high energy density for practical rechargeable batteries. P2-Na2/3Ni1/3Mn2/3O2 (hereafter denoted as P2-NiMn) is another candidate layered material which shows a high operating potential and high capacity density.4
P2-
Na2/3Ni1/3Mn2/3O2 (hereafter denoted as P2-NiMn) is another candidate layered material which shows a high operating potential and high capacity density.4 P2-NiMn delivers large
rechargeable capacity of ca. 160 mAh g-1.
The charge/discharge mechanism was
investigated with operando XRD and DFT calculations.4-5 P2-NiMn transforms into O2type phase by Na extraction on charge to 4.5 V and reversibly changes back into P2-type one by Na insertion on discharge to 2.0 V. Ni2+/4+ redox mainly contributes into the reaction and partial redox of oxide ion is predicted.5 However, its rechargeable capacity decays rapidly during charge/discharge cycles because the P2-O2 transition on the flat voltage plateau at 4.2 V during charge results in large volume shrinkage of 23% accompanied by gliding of Ni1/3Mn2/3O2 slabs to avoid strong electrostatic repulsion between oxide ions in the interslab space (see schematic illustration of the phase transition in Supporting Information, Figure S1), leading to electric isolation of P2-NiMn particles as reported in previous reports.5-8 Standard electrode potential of Na is ca. 0.3 V higher than that of Li, and the average working voltages of NaxMeO2 (Me = transition metals) in Na cells are generally lower than those of LixMeO2 in Li cells. Therefore, larger capacity is required for the positive electrode materials of Na cells than that of Li cells in order to achieve comparable energy density as Li-ion batteries by compensating the lower cell voltages for Na cells. To 3 ACS Paragon Plus Environment
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achieve larger capacity in NaxMeO2, operation in a wider potential range is necessary. The wider potential range and larger capacity lead to large volume change triggering electric isolation among active materials and conductive agent, and detachment of the composite layer from aluminum current collector, resulting in increase of electrode resistance and poor cyclability9-10. One of breakthrough ideas for this drawback of P2NiMn is to modify the material composition to suppress the volume change during charge/discharge cycles.11-18
For example, we have succeeded in mitigating volume
shrinkage of P2-NiMn during charging by proper amount of Cu or Ti substitution for Ni or
Mn,
respectively6,
19
,
and
enhancing
the
cyclability.
Specifically,
P2-
Na2/3Cu1/12Ni1/4Mn2/3O2 as a copper-substituted product and P2-Na2/3Ni1/3Mn1/2Ti1/6O2 as a titanium-substituted one for P2-NiMn show smaller volume-shrinkage ratios, defined as a ratio of lattice volumes between 4.5 V charged and pristine samples, 11% and 12%, respectively, compare to 23% of P2-NiMn. Our finding of P2-NiMn showing the large volume change during charge/discharge motivated us to adapt new binders for P2-NiMn electrodes.
Our group previously
demonstrated that the reversibility and cycle life of high-capacity electrochemical lithiation of Si-based negative electrodes was improved by applying water-soluble polysaccharide20,
sodium
poly-acrylate
(PAANa)21,
or
lithium
poly-ɤ-glutamate
(PGluLi)22 as the functional binder instead of PVdF. PGluLi has three times higher adhesion strength and the Si negative electrodes shows better electrochemical performances than PVdF22. Moreover, Si negative electrodes with sodium polyglutamate (PGluNa) or potassium polyglutamate (PGluK) binder show excellent electrochemical performances similar to those with PGluLi one22. The polyglutamate binders are greatly
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effective in enabling to improve the electrode performance accompanied by large volume change such as Si with a volume expansion of ca. 300% from Si to Li3.75Si by lithiation. Hence, new binder enhancing adhesion strength of the composite electrode and good electrical contact among active material, conductive agent, and current collector is most likely to improve electrochemical performance of P2-NiMn. Another critical properties responsible for the poor cyclability of P2-NiMn is surface reactivity involving electrolyte decomposition, especially at high voltage region above 4.1 V vs. Na, which leads to continuous low Coulombic efficiency during cycles.7 Recently, we reported that uniform coverage of PGluLi binder on Si particles effectively suppresses the electrolyte decomposition and improves cyclability of the Si/graphite composite negative electrodes for lithium-ion batteries22 unlike conventional PVdF binder. Therefore, it is expected that sodium poly-ɤ-glutamate (PGluNa) binder enhances cycle performance of P2-NiMn. To the best of our knowledge, almost all previous studies on positive electrode materials of sodium ion batteries reported so far are demonstrated with the composite electrode only with PVdF binder. In few papers, the effects of different binders on the electrochemical properties of layered positive electrode materials are described.7, 23-24 Since P2-NiMn has water-resistance property even by being exposed to humid air4, we apply water-soluble binders to P2-NiMn. Nevertheless, we find many papers claiming that it is impossible to apply water-soluble binder to layered positive electrode materials because of the damage by Na+/H+ exchange during water-slurry processing.7, 25 In this manuscript, we show that P2-NiMn electrode with water-soluble PGluNa binder demonstrates superior electrochemical performance to that with PVdF. Mechanism of the enhanced electrochemical property is investigated in detail by
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mechanical property measurements of the electrodes with PGluNa binder and surface analyses of P2-NiMn electrodes after charge and discharge cycle.
2. EXPERIMENTAL 2.1 Synthesis of Na2/3Ni1/3Mn2/3O2 Na2/3Ni1/3Mn2/3O2 was prepared by a solid-state reaction.
A stoichiometric mixture of
reagent grade Na2CO3 (Nacalai Tesque, Inc., 99.8%), Ni(OH)2 (Wako Pure Chemical Industries, Ltd., 95 %), and Mn2O3 prepared by heating MnCO3 (Kishida Chem. Co., Ltd., 44% as Mn content) at 700 oC were ball-milled with acetone for 12 h at 600 rpm. The mixture was dried and pressed into pellets, followed by heating at 900 oC for 24 h in air according to the previous report.4
2.2 Phase identification Phase purity of P2-type Na2/3Ni1/3Mn2/3O2 was confirmed by using an X-ray diffractometer (MultiFlex, Rigaku Co., Ltd.) equipped with a high-speed position sensitive detector (D/teX Ultra, Rigaku Co., Ltd.).
Non-monochromatized Cu Kα
radiation was utilized as an X-ray source with a nickel filter. The samples were set in a homemade air-tight sample holder during XRD measurement to avoid air exposure.
2.3 Preparation of composite electrodes Binders used in this study are as follows: PVdF (Polysciences, Inc.), sodium carboxymethyl cellulose (CMCNa, substitution degree = 0.8 – 1.0, Daicel Chemical Industries, Ltd.), and 6 ACS Paragon Plus Environment
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sodium poly-ɤ-glutamate (PGluNa). PGluNa was prepared by neutralizing poly-ɤ-glutamic acid (Wako Pure Chemical Industries, Ltd., molecular weight: 1500000 – 2500000 mol g-1) with stoichiometric amount of sodium hydroxide dissolved in deionized water.22 Their molecular structures are shown in Figure 1. Na2/3Ni1/3Mn2/3O2 powder and acetylene black (AB, Strem Chemicals, Inc.) were mixed at a weight ratio of 8 : 1 by using a mortar and pestle. Obtained mixed powder was further mixed with PVdF binder and adequate amount of N-methyl-2-pyrrolidone (NMP, Kanto Chemical Co., Ltd., Japan) to prepare slurry of P2-NiMn: AB: PVdF (= 8: 1: 1 w/w). The slurry was cast on Al foil with a doctor-blade and dried at 80 oC under vacuum. All processes for preparing PVdF electrodes were carried out in an Ar-filled glove box not to expose the samples to air. As for CMCNa and PGluNa electrodes, P2-NiMn and AB were mixed with each binder and adequate amount of deionized water to prepare aqueous slurry containing P2-NiMn : AB : binder = 8 : 1 : 1 (w/w) in atmosphere. The slurry was cast on Al foil with a doctor-blade and dried at 80 oC in air followed by drying at 150 oC under vacuum overnight. It is noted that slight decrease in the mass of CMCNa and PGluNa powder was observed below 200
o
C in air in the
thermogravimetric measurement (see Figure S2), indicating no significant decomposition and damage of the binder polymer during drying the electrodes at 150 oC.
2.4 Electrochemical measurements The electrochemical measurement was carried out by using R2032-type coin cells consisting of the working electrode of P2-NiMn, glass fiber filter as separator (GB-100R, ADVANTEC, Co.), electrolyte solution of 1.0 mol dm-3 NaPF6 dissolved in propylene carbonate (PC) (Kishida Chemical Co., Ltd.), and sodium metal (Purity > 99 %, Kanto Chemical Co., Ltd., Japan) as a 7 ACS Paragon Plus Environment
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counter electrode. Fabrication of the coin cells was carried out in an Ar-filled glove box. Galvanostatic charge-discharge test was conducted at ca. 25 oC in a voltage range of 2.0 – 4.5 V at C/20 (13.0 mA g-1) with a charge/discharge measurement system (TOSCAT-3100, TOYO System Co., Ltd.). Discharge-rate capability was evaluated from C/20 (13.0 mA g-1) to 2C (518 mA g-1). Self-discharging performance of the P2-NiMn composite electrodes was investigated by resting for 10 days after the 5th charging at C/20 up to 4.5 V.22 AC impedance measurement of the P2-NiMn composite electrodes were done with three electrode cells (TOYO System Co., Ltd.) after discharging to 3.5 V vs. Na+/Na in a frequency range from100 kHz to 10 mHz at an amplitude of 10 mV using a potentiostat/frequency response analyzer (VMP3 Multi-channel potentiostat, Bio-Logic Science Instruments Co., Ltd.).
2.5 Surface analysis of P2-NiMn electrodes X-ray photoelectron spectroscopy (XPS) was applied to analyze electrode surface with an Xray photoelectron spectrometer (JPS-9010MC, JEOL, Ltd.) with non-monochromatic Mg Kα used as an X-ray source. For the XPS, samples were prepared as follows. Coin cells after cycles were disassembled and the electrodes were rinsed moderately with diethyl carbonate (DEC) solvent. The rinsed electrodes were dried in Ar-filled glove box at room temperature overnight. Electrode surface morphology and particle distribution of P2-NiMn in the electrodes with PVdF and PGluNa binder were observed with a scanning electron microscope (SEM, JIB4500FE, JEOL Ltd.). Surface of the P2-NiMn particles in the tested electrodes was observed with a transmission electron microscope (TEM, JEM-2100F, JEOL Ltd.) at an accelerating voltage of 200 kV. For the TEM observation, samples were prepared as follows. Coin cells after
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cycles were disassembled and the composite layer was peeled off from aluminum collector and the composite layer was dispersed in dehydrated ethanol.
2.6 Evaluation of mechanical properties for P2-NiMn electrodes Adhesive strength of the P2-NiMn composite layer formed on aluminum foil was measured with a peel tester (STA-1150, A&D Co., Ltd.) and double-side tape (Scotch tape, SPS-12, 3M Japan, Ltd.) referring to the previous report.22
The measurement
conditions are as follows: 90 degrees for peeling angle, 10 mm min−1 for peeling speed, and 50 N for load range. A simplified peel test was also performed with an adhesive tape (Cellotape, CT-18, NICHIBAN Co., Ltd.).
And also scratch test of the PVdF and
PGluNa electrodes was performed with Surface And Interfacial Cutting Analysis System (SAICAS) (DN-GS, DAYPLA WINTES Co., Ltd.).26-27
The measurement was
performed in constant speed mode at horizontal and vertical velocities of 2 and 0.1µm s-1, respectively. Cutting depth was around 10 µm for both PVdF and PGluNa electrodes. The cutting blade was made of boron nitride with a cutting edge of 1 mm wide. The PVdF and PGluNa electrodes were immersed in propylene carbonate (PC) overnight at room temperature before the scratch test to simulate actual electrodes filled with electrolyte solution.
2.7 Evaluation of physical properties for PVdF, CMCNa, and PGluNa Thermal stability of PVdF, CMCNa, and PGluNa powder was examined by using a thermogravimetry (TG, DTG-60, Shimadzu Corporation). The TG analysis was performed in air at a heating speed of 5 °C min-1.
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Electrolyte absorption rate of PVdF, CMCNa, and PGluNa was examined by immersing the pure binder films in propylene carbonate for one day. The rate was quantified based on the weight gain of the films before and after immersion in propylene carbonate according to the following formula.28
/% =
/ − / × () /
3. RESULTS AND DISCUSSION 3.1 Binder dependency of electrochemical properties P2-NiMn is known to show no change of the XRD pattern when exposed to humid air.4 To survey compatibility of P2-NiMn with water as dispersion medium for water-soluble binder, structural stability of P2-NiMn was investigated by soaking the P2-NiMn in water. Figure 2 shows XRD patterns of P2-NiMn before and after immersing in water for one year. Before immersing the P2-NiMn sample synthesized, all diffraction lines can be indexed as P2-type structure with space group of P63/mmc expect for 1/6 2/3 1/3 and 1/6 2/3 2/3 superlattice peaks at 27.5° and 28.6° in 2 θ , respectively.
The lattice
parameters are coincident with those in the literatures4-5 (see Table S1).
Even after
immersing for one year, all diffraction lines can be indexed as P2-type structure, and no evidence of hydrated phase and decomposition is found unlike P2-Na2/3CoO229 or P2Na2/3Co1/3Mn2/3O2.30 The lattice parameters of a- and c-axis were almost unchanged after immersing (see Table S1), indicating that the original P2-type structure was maintained. Moreover, full width at half maximum (FWHM) of 002 and 004 peaks is also almost the 10 ACS Paragon Plus Environment
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same before and after immersion (see Table S1), suggesting no change in crystallite size and lattice distortion before and after immersing for one year.
Consequently, it is
explicitly demonstrated that P2-NiMn is enough stable against water and water-soluble binder is applicable to P2-NiMn. Herein, CMCNa, which is a well-known water-soluble binder for positive and negative electrodes in lithium-ion batteries,31-32 and PGluNa as a new water-soluble binder is chosen to evaluate the binder effect on the electrochemical performance of P2-NiMn electrodes comparing with PVdF binder. Figures 3(a-c) present galvanostatic charge and discharge curves of P2-NiMn electrodes with PVdF, CMCNa, and PGluNa binders tested in the voltage range of 2.0 4.5 V. The PVdF electrode in Figure 3(a) shows the largest discharge capacity of 165 mAh g-1 among the electrodes and obviously flat voltage plateaus are observed at 4.2 and 4.0 V on the first charge and discharge, respectively. However, the flat voltage plateaus gradually become sloping profiles with larger polarization during charge/discharge cycles and the capacity on the plateau region above 4.0 V simultaneously degraded. On the other hand, the CMCNa and PGluNa electrodes in Figures 3(b) and 3(c) show discharge capacity of 155 and 151 mAh g-1 with nearly flat voltage plateaus above 4.0 V at the same potential in the initial curves. The voltage plateaus become sloping profiles during cycles which is similar to the PVdF electrode.
Both the CMCNa and PGluNa electrodes,
however, show no significant increase of polarization on the plateau region during cycles, resulting in improved capacity retention rate of 86% and 89%, respectively, after 50 cycles compared to 71% of the PVdF electrode, as shown in Figure 3(d). Moreover, initial Coulombic efficiencies of the CMCNa and PGluNa electrodes are 92% and 95%, respectively, which is much higher than 80% of the PVdF electrode. This result suggests
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that electrolyte decomposition at high voltage region above 4.0 V and/or electrical isolation of the P2-NiMn particles could be to some degree prevented by utilizing the CMCNa or PGluNa binder compared to the PVdF electrode.
Serious capacity
degradation of P2-NiMn during cycles was previously reported for the electrode with a PVdF binder when the upper cut-off voltage was as high as 4.5 V in the Na cells 5, 7, 33 and similar results are obtained in this study. It should be noted that the better capacity retentions of the CMCNa and PGluNa electrodes are not due to their smaller capacities because their cycle tests with the charge capacity limited to 140 mAh g-1 in 2.0 – 4.5 V revealed faster decay in discharge capacity for the PVdF electrode than that of the PGluNa one although Coulombic efficiency is almost same (see Figure S3). PGluNa and CMCNa electrodes also achieves better rate capability than PVdF one as shown in Figure 3(f). Indeed, the CMCNa and PGluNa electrodes show discharge capacity of 150 mAh g1
slightly lower than 160 mAh g-1 of the PVdF one at a low rate of C/20 in Figure 3 and
volume change of P2-NiMn could be one of the influencing factors. The difference, however, decreases gradually with increase in discharge rate from C/20 to 1C. Discharge capacity of the PGluNa and CMCNa electrodes exceeded that of the PVdF one at 2C. The superior rate performance is thought to result from lower resistance and better mechanical durability of the composite layer with the PGluNa and CMCNa binder than those in PVdF one. Static electrochemical performance is also examined by self-discharge test. Figure 4 shows variation in Coulombic efficiency of the PVdF, CMCNa, and PGluNa electrodes during cycles through storage for 10 days in open circuit after 5th charge to 4.5 V at room temperature. The PGluNa electrode shows 82% of Coulombic efficiency at the 5th cycle,
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which is higher than 72% of the PVdF one. Order of the Coulombic efficiency in the self-discharge test among the PVdF, CMCNa, and PGluNa electrodes is consistent with 1st Coulombic efficiency mentioned in Figure 3(e). The PGluNa electrode shows the highest efficiencies, which implies that PGluNa binder suppresses electrolyte decomposition during charge/discharge cycles and storage at high potential. We believe that the suppression of electrolyte decomposition is attributed to improved passivation by covering the P2-NiMn particle surface with PGluNa thin coating as described in our paper.22 In all the electrochemical measurements, the PGluNa electrode clearly exhibits better electrochemical performances in terms of capacity retention, Coulombic efficiency, rate capability, and self-discharge. Not only the kinetics of Na (de)intercalation into P2-NiMn but also passivation of the composite electrode are superior in the PGluNa electrode. We further evaluated the PVdF and PGluNa electrodes by AC impedance measurement. Figure 5 shows nyquist plots of the PVdF and PGluNa electrodes discharged to 3.5 V.
It is difficult to clearly deconvolute the semicircles and assign into electrolyte,
surface, charge-transfer, and contact resistances by refining the Nyquist plot. Therefore, we discuss the results simply with assignment of the semicircles as total electrode resistance for a P2-NiMn electrode in the three-electrode cell. The PVdF electrode in Figure 5(a) shows gradual increase in diameter of the semicircle indicating that the total resistance gradually becomes large upon cycles. On the other hand, the PGluNa electrode in Figure 5(b) exhibits small and almost constant diameter of semicircles during cycles and no significant increase in the total resistance is observed for 30 cycles. These results mean that the PGluNa electrode shows much lower electrode resistance than that of the
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PVdF one during cycles. Two mechanisms can be proposed for the lower resistance of the PGluNa electrode. One is lower surface and charge-transfer resistance by suppression of electrolyte decomposition and less deposition of the decomposition products on surface of the P2-NiMn particles.
Surface structure of the P2-NiMn particles might be also
maintained as reported for Al2O3-coated P2-NiMn.34-35
The other is lower contact
resistance due to suppressed electrical isolation of the P2-NiMn particles in the composite electrode by high adhesion strength of the PGluNa binder. To prove the hypotheses, surface and mechanical properties of the PGluNa and PVdF electrodes and physical properties of the PGluNa and PVdF polymers were further investigated as described below.
3.2 Surface analysis of electrodes X-ray photoelectron spectroscopy (XPS) measurement was carried out to investigate coverage of the PGluNa binder on the P2-NiMn particles in the electrodes. Three pristine PGluNa electrodes were prepared at different PGluNa content, x = 2, 5, and 10 in P2NiMn: AB: PGluNa (= 80: 10: x w/w). O 1s spectra in Figure 6(a) show a peaks at 529 eV in binding energy assigned to lattice oxygen of Na2/3[Ni1/3Mn2/3]O236, and peaks at higher binding energy between 531 and 533 attributed to sodium carbonate on surface of P2-NiMn, and peptide bond (-O=C-N-) and sodium carboxylate (-COONa) in PGluNa.3637
Relative intensity of the former peak of lattice oxygen decreases while those of the
peaks of PGluNa increase with increase in the PGluNa content, which indicates that content of the lattice oxygen decreases and that of PGluNa increases at surface of the electrodes as PGluNa content increases in the surface layer within a few-nanometer depth.
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C 1s spectra in Figure 6(b) show decrease in intensity of the peaks at 284 eV attributed to sp2 hybridized carbon (-C-C-) in AB as PGluNa content increases, while intensity of peaks observed at 286, 288, and 291 eV, assigned to -C-N-, peptide bond (-O=C-N-)37, and sodium carboxylate (-COONa)22, respectively, becomes higher, which suggests decrease in AB content with increase in PGluNa at surface of the electrodes. From these results, it is most likely that surface of the P2-NiMn and AB particles is progressively covered with the increase in PGluNa binder content. As expected, better cycle stability is observed for the 80:10:10 electrode than that of the 80:10:2 one (as seen in Figure S4), which should be due to the improvement of surface passivation. On the basis of the XPS results for the PGluNa electrodes, we compare XPS spectra of the P2-NiMn electrodes with PVdF or PGluNa binder.
No significant difference of
particle distribution and morphology for P2-NiMn is confirmed in SEM images for the PVdF or PGluNa electrodes before and after 50cycles (see Figure S5). Figure 7(a) shows O 1s XPS spectra of pristine PVdF and PGluNa electrodes.
In the PGluNa
electrode, a peak of lattice oxygen at 529 eV is weak and peaks attributed to sodium carbonate and sodium carboxylate at 532 and 533 eV, respectively, are stronger as mentioned for the 80:10:10 electrode above, while the PVdF electrode shows a stronger peak of lattice oxygen at 529 eV. This difference suggests that surface of the P2-NiMn particles in the PGluNa electrode is more covered than that in the PVdF one. Figure 7(b) presents C 1s spectra of pristine PVdF and PGluNa electrodes. Although we find no difference in intensity of a peak at 284 eV corresponding to AB in the Figure, the peaks at 286, 288, and 291 eV attributed to PGluNa binder clearly appear compared with those of PVdF binder. Furthermore, Mn 2p1/2 and 2p3/2 peaks at 654 and 642 eV, respectively,
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are very weak for the PGluNa electrode, while those for the PVdF electrode are quite clear and the intensity is much higher in Figure 7(c). The result of all the XPS spectra in Figure 7 clearly indicates that PGluNa binder thin coating is formed on P2-NiMn and AB particles more than PVdF one in the pristine electrodes, which is consistent of our observation in Si-graphite composite electrode with PGluNa and PVdF binders as already described. According to our previous observations,22 PGluNa should be amorphous after drying the slurry on Al foil considering our evidence of formation of amorphous lithium polyglutamate film, which is advantage of homogeneous coverage on the whole surface of P2-NiMn. Additionally, lone pair of electrons of not only oxygen but also nitrogen atoms of PGluNa are possibly capable to form coordinate bond with Li+ ions to induce desolvation of solvated Li+ ions.22, 38 Similar desolvation of solvated Na+ ions possibly occurs at the P2-NiMn electrode with the functional binder of PGluNa to enhance the Na+ diffusion across the interface of P2-NiMn and electrolyte, which should affect the much lower impedance of the PGluNa electrode as shown in Figure 5. We further investigate surface of the P2-NiMn electrodes with PVdF or PGluNa binder after charge/discharge. Figure 8 shows Mn 2p, O 1s, and C 1s XPS spectra of the PVdF and PGluNa electrodes after the 1st and the 10th cycle. In the PVdF electrodes (Figures 8 (a-c)), no significant difference is observed for Mn 2p1/2 and 2p3/2 peaks between the 1st and 10th cycle (Figure 8(a)), which evidences that the P2-NiMn particles remain to be exposed to electrolyte even after 10 cycles in the PVdF electrode. O 1s spectra in Figure 8(b) also supports no significant change of lattice-oxygen peak at 529 eV. However, stronger peaks are observed at 533 – 534 eV attributed to electrolyte decomposition products such as oxygenated and carbonaceous species (-COONa, -C=O-).36 Furthermore,
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C1s spectra in Figure 8(c) also show weaker AB peak at 284 eV and -CH2-CF2- one at 291 eV after the 10th cycle. These results for the PVdF electrodes suggest accumulation of decomposition products mainly on surface of AB, and surface of the P2-NiMn particles is not covered with the decomposition products. On the other hand, Mn 2p1/2 and 2p3/2, O1s, and C 1s spectra of the PGluNa electrode in Figure 8(d-f) show no significant change of peaks between the 1st and the 10th cycle, which suggests that coverage with PGluNa on the P2-NiMn particles is kept and PGluNa binder passivates the P2-NiMn particles during charge/discharge cycles. We believe that the PGluNa binder maintains stable surface of the composite electrode during charge/discharge cycles due to suppression of electrolyte decomposition. It is worth mentioning that the PGluNa binder covers surface of the P2-NiMn and AB particles and assists for formation of the stable passivation layer, which is consistent of the better cycle stability, better rate-performance, higher Coulombic efficiency, and lower electrode resistance during cycles as mentioned above. Furthermore, we investigated surface condition of the P2-NiMn particles with TEM. Figure 9 shows TEM bright field images of the P2-NiMn particles in the PVdF or PGluNa electrodes before and after 10 and 30 cycles. Pristine PVdF electrode shows smooth surface of P2-NiMn particles with clear lattice fringe. However, quite rough surface with some holes and pockets is observed after 10 cycles, and cleavage is also formed after 30 cycles. On the other hand, surface of P2-NiMn in the PGluNa electrode shown in Figure 8(b) presents no remarkable change even after 30 cycles as similar as reported previously for LiCoO2 (LCO)39, in which coverage of LCO particles with SBRCMCNa binder and deterioration of the LCO surface after high-voltage cycles is
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sufficiently suppressed.
Similarly, PGluNa binder coverage would protect P2-NiMn
particles against high-voltage damage, such as electrolyte decomposition and corrosive dissolution of P2-NiMn, which is quite consistent with the XPS results described above. The positive effects of the surface coverage of P2-NiMn on the electrode performance were previously reported with Al2O3-coating34-35 and surface treatment such as binder coverage and ceramic coating, these methodology would be also applicable for highvoltage electrode materials in Na-ion batteries. In addition to the surface coverage, high adhesion strength of the PGluNa binder is expected to be synergic origin of the better performances such as better cycle stability, better rate-performance, higher Coulombic efficiency, and lower electrode resistance during cycles as mentioned above. Therefore, mechanical properties of the PGluNa electrodes and PGluNa polymer were examined and the results are discussed in the next section.
3.3 Mechanical properties of PGluNa electrode and PGluNa polymer Vertically peeling test was conducted based on our previous paper21 as shown in Figure 10(a), to measure the adhesion strength between composite layer and aluminum current collector. The results shown in Figure 10(b) confirms the obvious difference of adhesion strength between the PVdF and PGluNa electrodes. When they were peeled at speed of 10 mm min-1, the PGluNa electrode was peeled off with load intensity of 2.75 N cm-1 on average, corresponding to 180 times adhesion strength of the PVdF electrode of 0.0154 N cm-1. After peel test, most of the composite layer of the PVdF electrode was totally removed from the aluminum foil without any black residue, while the composite layer of the PGluNa electrode was not peeled off from the aluminum foil as shown in
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Figure 10(c), suggesting that the PGluNa binder contributes the considerably higher adhesion strength than that of the PVdF electrode, agreeing with our previous study.22 The results also indicate that adhesion strength measured for the PGluNa electrode by 90o peel test in Figure 10(b) is corresponding to the strength between the composite layer and double-side tape. Actual adhesion strength of PGluNa binding between composite layer and aluminum current collector is extremely high and could not measure in our experimental condition. In addition, preliminary bending test for the PVdF and PGluNa electrodes, of which details are shown in Figure S6, convinces higher adhesion strength and flexibility of the PGluNa electrode than that of the PVdF one. These adhesion tests were conducted in dry condition without immersing in electrolyte, but the adhesion strength of dried electrodes is not the same as wet electrode with organic electrolyte solution. Therefore, another peel test with an adhesive tape was carried out for the PVdF and PGluNa electrodes with or without immersion in 1 mol dm-3 NaPF6 / PC electrolyte solution as shown in Figure S7. The PVdF electrodes show obvious difference with and without soaking in the electrolyte, and complete and partial detachment of PVdF composite layer from Al foil, respectively. On the other hand, no detachment of PGluNa composite layer from Al current collector is observed with or without immersing in the electrolyte, convincing higher adhesion strength of the PGluNa electrodes than the PVdF one even after soaking in the electrolyte. Quantitative analysis of adhesion strength for the PVdF and PGluNa electrodes was further conducted in wet condition with electrolyte solvent. Wet PVdF and PGluNa electrodes with PC were used simulating actual wet electrodes in the cells. The adhesion strength is evaluated by using SAICAS27, 40 and horizontal force is detected during slicing
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the composite layer in the electrodes at the depth of 10 µm by using a boron nitride blade (width: 1 mm) (see photos of the electrode and blade during the operation in Figures 11(a-b)). Although the surface morphologies of the pristine PVdF and PGluNa electrodes were almost the same in appearance in the SEM images (as described above in Figure S5), the electrodes reveal different load intensities along horizontal direction in Figures 11(c-d). Average cutting load of the PVdF electrode is 0.026 N, while that of the PGluNa electrode is 1.27 N about 50 times higher than that of the PVdF one. The higher adhesion strength of the wet PGluNa electrode than the PVdF one is almost identical with the results of peel test with or without soaking in electrolyte.
The results suggest that
PGluNa binder has higher adhesion strength not only at the interface between the composite and Al foil but also of the inside of the composite, i.e. particle binding among P2-NiMn and AB particles, compared to those for the PVdF binder. It is reasonably believed that the high adhesion strength of the PGluNa binder is highly beneficial to suppress electrical isolation of the electrode materials during cycling accompanied with the large volume change of ca. 20%,4,
6, 19
resulting in the excellent electrochemical
performance of the P2-NiMn electrodes. Another factor which affects adhesion characteristics is electrolyte absorption of binder. Too much uptake of electrolyte solution inside the composite would lead to poor electronical connection among the P2-NiMn28 and AB particles and current collector. No electrolyte absorption, on the contrary, surely lead to poor electrode performance, because diffusion route of Na+ ions would be restricted and redox reaction of P2-NiMn would be deteriorated, resulting in poor ionic diffusion and high electrode resistance.
For the
electrolyte absorption test, pure polymer films of PVdF, CMCNa, and PGluNa prepared
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by casting and drying the polymer solution (see Figure S8) were immersed in PC for one day in an Ar-filled grove box. Weight gain of the films was compared before and after storage in PC and electrolyte absorption rate was calculated as compared in Figure 12. The PGluNa and CMCNa films show electrolyte absorption rate of 3.5% and 18%, respectively, lower than 25.5% of PVdF.
The much lower and moderate electrolyte
absorption rate of PGluNa binder is advantageous to realize optimum balance of the Na+ ion diffusion and electric solid-contact between P2-NiMn, AB, and Al foil for the superior performance of P2-NiMn. To sum up the mechanical properties of PGluNa polymer and the P2-NiMn electrode, the moderate electrolyte penetration and higher adhesion strength of PGluNa binder contribute to reversible sodium insertion / extraction and cycle stability of P2-NiMn with suppression of electrolyte decomposition on surface of the PGluNa coated P2-NiMn, and detachment and electrical isolation of the P2-NiMn particles, resulting in low initial Coulombic efficiency, better cycle and rate stability of the P2-NiMn composite electrodes in Na batteries compared to conventional PVdF binder. Considering the above discussion and results, what is elucidated in this study is illustrated in Figure 13.
In the PVdF electrode, electrolyte decomposition products
deposit on the P2-NiMn particles and surface structure deteriorates gradually during cycles. And also electrical isolation among the P2-NiMn particles, AB ones, and Al current collector due to the large volume change of P2-NiMn during charge/discharge increases the total electrode resistance and accelerates capacity decay during cycles. On the other hand, the PGluNa electrode in which PGluNa covers surface of P2-NiMn particles and the coverage film has less electrolyte swelling than PVdF, provides stable
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surface structure and better electrochemical performance as exhibited in Figures 3, 4, and 5. Functional binders acting as a passivation layer with ionic conductivity and an highly adhesive binder such as CMCNa and PGluNa should be a key factor for not only negative electrode materials but also positive ones14, 41-46 to enhance the electrochemical properties of the electrode materials in Li-, Na-, and K-ion batteries, and thus battery performance would be upgraded by applying a proper functional binder.
4. CONCLUSION We applies water-soluble binders of CMCNa and PGluNa to P2-Na2/3Ni1/3Mn2/3O2 composite electrodes for high-voltage sodium-ion batteries. The PGluNa electrodes show superior electrochemical properties in terms of reversible capacity, Coulombic efficiency, capacity retention, and rate capability compared to the PVdF electrodes. The PGluNa binder is efficient to suppress self-discharge because of surface coverage of the P2-NiMn particles with PGluNa thin layer and suppression of both electrolyte decomposition and corrosive deterioration of the oxide.
Moreover, the PGluNa electrodes realize much
lower electrode resistance during cycles than the PVdF ones, which should be due to the higher adhesion strength and the moderate electrolyte penetration leading to suppressed electrical isolation of the P2-NiMn particles induced by the volume change of P2-NiMn. Finding of the efficient binder towards high-voltage layered sodium transition metal oxides paves a new way to improve electrode performance of high-voltage positive electrode materials for sodium-ion batteries instead of a conventional PVdF binder. However, all the results in this study are collected for simple P2-NiMn without modification of the composition. Therefore, combination of partial metal-substitution and 22 ACS Paragon Plus Environment
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PGluNa binder for the P2-NiMn will lead to further enhancement of electrochemical performance of the P2-NiMn positive electrodes for sodium-ion batteries.
ASSOCIATED CONTENT Supporting Information. Lattice parameters of Na2/3Ni1/3Mn2/3O2, TG curves of binder powder, charge–discharge curves of Na/P2-NiMn cells in limited charge capacity, capacity retention of PVdF (= 80:10:10 w/w), PGluNa (80:10:10 w/w), and PGluNa (80:10:2 w/w) electrodes, photos of the electrodes after bending test, photos of peel tests, SEM images, and photos of binder films.
AUTHOR INFORMATION Corresponding Author *E-mail:
[email protected] ACKNOWLEDGEMENT This study was in part supported by Adaptable and Seamless Technology Transfer Program (A-STEP) of JST. The authors thank Dr. Ichihashi and Prof. Idemoto, TUS, for TEM measurements.
REFERENCES (1) Li, Y.; Yang, Z.; Xu, S.; Mu, L.; Gu, L.; Hu, Y. S.; Li, H.; Chen, L. Air‐Stable Copper‐ Based P2‐Na7/9Cu2/9Fe1/9Mn2/3O2 as a New Positive Electrode Material for Sodium‐Ion Batteries. Adv. Sci. 2015, 2, 150031. 23 ACS Paragon Plus Environment
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(2) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research Development on Sodium-Ion Batteries. Chem. Rev. 2014, 114, 11636-11682. (3) Yabuuchi, N.; Kajiyama, M.; Iwatate, J.; Nishikawa, H.; Hitomi, S.; Okuyama, R.; Usui, R.; Yamada, Y.; Komaba, S. P2-type Na x [Fe 1/2 Mn 1/2] O 2 Made from Earth-Abundant Elements for Rechargeable Na Batteries. Nat. Mater. 2012, 11, 512. (4) Lu, Z.; Dahn, J. R. In Situ X-Ray Diffraction Study of P2-Na 2/3Ni[1/3Mn2/3]O2. J. Electrochem. Soc. 2001, 148, A1225-A1229. (5) Lee, D. H.; Xu, J.; Meng, Y. S. An Advanced Cathode for Na-ion Batteries with High Rate and Excellent Structural Stability. Phys. Chem. Chem. Phys. 2013, 15, 3304-3312. (6) Yoshida, H.; Yabuuchi, N.; Kubota, K.; Ikeuchi, I.; Garsuch, A.; Schulz-Dobrick, M.; Komaba, S. P2-type Na2/3Ni1/3Mn2/3−xTixO2 as a New Positive Electrode for Higher Energy Na-ion Batteries. Chem. Commun. 2014, 50, 3677-3680. (7) Kubota, K.; Komaba, S. Review—Practical Issues and Future Perspective for Na-Ion Batteries. J. Electrochem. Soc. 2015, 162, A2538-A2550. (8) Kubota, K.; Kumakura, S.; Yoda, Y.; Kuroki, K.; Komaba, S. Electrochemistry and SolidState Chemistry of NaMeO2 (Me = 3d transition metals). Adv. Energy Mater. 2018, Under revision. (9) de la Llave, E.; Borgel, V.; Park, K.-J.; Hwang, J.-Y.; Sun, Y.-K.; Hartmann, P.; Chesneau, F.-F.; Aurbach, D. Comparison between Na-Ion and Li-Ion Cells: Understanding the Critical Role of the Cathodes Stability and the Anodes Pretreatment on the Cells Behavior. ACS Appl. Mater. Interfaces 2016, 8, 1867-1875. (10) de la Llave, E.; Talaie, E.; Levi, E.; Nayak, P. K.; Dixit, M.; Rao, P. T.; Hartmann, P.; Chesneau, F.; Major, D. T.; Greenstein, M.; Aurbach, D.; Nazar, L. F. Improving Energy Density
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and Structural Stability of Manganese Oxide Cathodes for Na-Ion Batteries by Structural Lithium Substitution. Chem. Mater. 2016, 28, 9064-9076. (11) Clément, R. J.; Billaud, J.; Armstrong, A. R.; Singh, G.; Rojo, T.; Bruce, P. G.; Grey, C. P. Structurally Stable Mg-doped P2-Na 2/3 Mn 1− y Mg y O 2 Sodium-ion Battery Cathodes with High Rate Performance: Insights from Electrochemical, NMR and Diffraction Studies. Energy Environ. Sci. 2016, 9, 3240-3251. (12) Wang, P.-F.; You, Y.; Yin, Y.-X.; Wang, Y.-S.; Wan, L.-J.; Gu, L.; Guo, Y.-G. Suppressing the P2-O2 Phase Transition of Na0.67Mn0.67Ni0.33O2 by Magnesium Substitution for Improved Sodium-Ion Batteries. Angew. Chem., Int. Ed. 2016, 55, 7445-7449. (13) Hou, H.; Gan, B.; Gong, Y.; Chen, N.; Sun, C. P2-Type Na0.67Ni0.23Mg0.1Mn0.67O2 as a High-Performance Cathode for a Sodium-Ion Battery. Inorg. Chem. 2016, 55, 9033-9037. (14) Zhang, W.; Dahbi, M.; Komaba, S. Polymer Binder: A Key Component in Negative Electrodes for High-energy Na-ion Batteries. Curr. Opin. Chem. Eng. 2016, 13, 36-44. (15) Wu, X.; Xu, G.-L.; Zhong, G.; Gong, Z.; McDonald, M. J.; Zheng, S.; Fu, R.; Chen, Z.; Amine, K.; Yang, Y. Insights into the Effects of Zinc Doping on Structural Phase Transition of P2-Type Sodium Nickel Manganese Oxide Cathodes for High-Energy Sodium Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8, 22227-22237. (16) Wu, X.; Guo, J.; Wang, D.; Zhong, G.; McDonald, M. J.; Yang, Y. P2-type Na0.66Ni0.33– xZnxMn0.67O2 as New High-voltage Cathode Materials for Sodium-ion Batteries. J. Power Sources 2015, 281, 18-26. (17) Wang, L.; Sun, Y.-G.; Hu, L.-L.; Piao, J.-Y.; Guo, J.; Manthiram, A.; Ma, J.; Cao, A.-M. Copper-substituted Na 0.67 Ni 0.3− x Cu x Mn 0.7 O 2 Cathode materials for Sodium-ion Batteries with Suppressed P2–O2 Phase Transition. J. Mater. Chem. A 2017, 5, 8752–8761.
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(18) Zheng, L.; Li, J.; Obrovac, M. Crystal Structures and Electrochemical Performance of AirStable Na2/3Ni1/3–x Cu x Mn2/3O2 in Sodium Cells. Chem. Mater. 2017, 29, 1623-1631. (19) Kubota, K.; Yoda, Y.; Komaba, S. Origin of Enhanced Capacity Retention of P2-Type Na2/3 Ni1/3-xMn2/3CuxO2 for Na-Ion Batteries. J. Electrochem. Soc. 2017, 164, A2368A2373. (20) Murase, M.; Yabuuchi, N.; Han, Z.-J.; Son, J.-Y.; Cui, Y.-T.; Oji, H.; Komaba, S. CropDerived Polysaccharides as Binders for High-Capacity Silicon/Graphite-Based Electrodes in Lithium-Ion Batteries. ChemSusChem 2012, 5, 2307-2311. (21) Komaba, S.; Yabuuchi, N.; Ozeki, T.; Han, Z.-J.; Shimomura, K.; Yui, H.; Katayama, Y.; Miura, T. Comparative Study of Sodium Polyacrylate and Poly(vinylidene fluoride) as Binders for High Capacity Si–Graphite Composite Negative Electrodes in Li-Ion Batteries. J. Phys. Chem. C 2012, 116, 1380-1389. (22) Mochizuki, T.; Aoki, S.; Horiba, T.; Schulz-Dobrick, M.; Han, Z.-J.; Fukuyama, S.; Oji, H.; Yasuno, S.; Komaba, S. “Natto” Binder of Poly-γ-glutamate Enabling to Enhance Silicon/Graphite Composite Electrode Performance for Lithium-Ion Batteries. ACS Sustainable Chem. Eng. 2017, 5, 6343-6355. (23) Dall’Asta, V.; Buchholz, D.; Chagas, L. G.; Dou, X.; Ferrara, C.; Quartarone, E.; Tealdi, C.; Passerini, S. Aqueous Processing of Na0.44MnO2 Cathode Material for the Development of Greener Na-Ion Batteries. ACS Appl. Mater. Interfaces 2017, 9, 34891-34899. (24) Zhang, X.-H.; Pang, W.-L.; Wan, F.; Guo, J.-Z.; Lü, H.-Y.; Li, J.-Y.; Xing, Y.-M.; Zhang, J.-P.; Wu, X.-L. P2–Na2/3Ni1/3Mn5/9Al1/9O2 Microparticles as Superior Cathode Material for Sodium-Ion Batteries: Enhanced Properties and Mechanisam via Graphene Connection. ACS Appl. Mater. Interfaces 2016, 8, 20650-20659.
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(25) Muller-Bouvet, D.; Baddour-Hadjean, R.; Tanabe, M.; Huynh, L.; Le, M.; Pereira-Ramos, J. Electrochemically Formed α’-NaV2O5: A New Sodium Intercalation Compound. Electrochim. Acta 2015, 176, 586-593. (26) Son, B.; Ryou, M.-H.; Choi, J.; Lee, T.; Yu, H. K.; Kim, J. H.; Lee, Y. M. Measurement and Analysis of Adhesion Property of Lithium-Ion Battery Electrodes with SAICAS. ACS Appl. Mater. Interfaces 2013, 6, 526-531. (27) Nishiyama, I.; Saito, M. Study on Depth Profiling Mechanical Property by Surface and Interfacial Cutting Method. J. Print. Sci. Technol. 2005, 42, 27-31. (28) Ugawa, S.; Masuda, K.; Kajiwara, I. Water-Based Binder for LIB Application. JSR Tech. Rev. 2014, 121, 10-15. (29) Takada, K.; Sakurai, H.; Takayama-Muromachi, E.; Izumi, F.; Dilanian, R. A.; Sasaki, T. Superconductivity in Two-dimensional CoO2 Layers. Nature 2003, 422, 53-55. (30) Lu, Z.; Dahn, J. R. Intercalation of Water in P2, T2 and O2 Structure Az[CoxNi1/3xMn2/3]O2. Chem. Mater. 2001, 13, 1252-1257. (31) Li, J.; Lewis, R. B.; Dahn, J. R. Sodium Carboxymethyl Cellulose A Potential Binder for Si Negative Electrodes for Li-Ion Batteries Electrochem. Solid-State Lett. 2007, 10, A17-A20. (32) Wang, Z.; Dupré, N.; Gaillot, A.-C.; Lestriez, B.; Martin, J.-F.; Daniel, L.; Patoux, S.; Guyomard, D. CMC as a Binder in LiNi0.4Mn1.6O4 5V Cathodes and Their Electrochemical Performance for Li-ion Batteries. Electrochim. Acta 2012, 62, 77-83. (33) Kalapsazova, M.; Ortiz, G. F.; Tirado, J. L.; Dolotko, O.; Zhecheva, E.; Nihtianova, D.; Mihaylov, L.; Stoyanova, R. P3-Type Layered Sodium-Deficient Nickel-Manganese Oxides: A Flexible Structural Matrix for Reversible Sodium and Lithium Intercalation. ChemPlusChem 2015, 80, 1642-1656.
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(34) Liu, Y.; Fang, X.; Zhang, A.; Shen, C.; Liu, Q.; Enaya, H. A.; Zhou, C. Layered P2Na2/3[Ni1/3Mn2/3]O2 as High-voltage Cathode for Sodium-ion Batteries: The Capacity Decay Mechanism and Al2O3 Surface Modification. Nano Energy 2016, 27, 27-34. (35) Alvarado, J.; Ma, C.; Wang, S.; Nguyen, K.; Kodur, M.; Meng, Y. S. Improvement of the Cathode Electrolyte Interphase on P2-Na2/3Ni1/3Mn2/3O2 by Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2017, 9, 26518-26530. (36) Doubaji, S.; Philippe, B.; Saadoune, I.; Gorgoi, M.; Gustafsson, T.; Solhy, A.; Valvo, M.; Rensmo, H.; Edström, K. Passivation Layer and Cathodic Redox Reactions in Sodium-Ion Batteries Probed by HAXPES. ChemSusChem 2016, 9, 97-108. (37) Chen, W.; Qian, T.; Xiong, J.; Xu, N.; Liu, X.; Liu, J.; Zhou, J.; Shen, X.; Yang, T.; Chen, Y.; Yan, C. A New Type of Multifunctional Polar Binder: Toward Practical Application of High Energy Lithium Sulfur Batteries. Adv. Mater. 2017, 29, 1605160. (38) Komaba, S.; Yabuuchi, N.; Ozeki, T.; Okushi, K.; Yui, H.; Konno, K.; Katayama, Y.; Miura, T. Functional Binders for Reversible Lithium Intercalation into Graphite in Propylene Carbonate and Ionic Liquid Media. J. Power Sources 2010, 195, 6069-6074. (39) Yabuuchi, N.; Kinoshita, Y.; Misaki, K.; Matsuyama, T.; Komaba, S. Electrochemical Properties of LiCoO2 Electrodes with Latex Binders on High-Voltage Exposure. J. Electrochem. Soc. 2015, 162, A538-A544. (40) Son, B.; Ryou, M.-H.; Choi, J.; Lee, T.; Yu, H. K.; Kim, J. H.; Lee, Y. M. Measurement and Analysis of Adhesion Property of Lithium-Ion Battery Electrodes with SAICAS. ACS Appl. Mater. Interfaces 2014, 6, 526-531. (41) Dahbi, M.; Yabuuchi, N.; Kubota, K.; Tokiwa, K.; Komaba, S. Negative electrodes for Naion batteries. Phys. Chem. Chem. Phys. 2014, 16, 15007-15028.
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(42) Fukunishi, M.; Yabuuchi, N.; Dahbi, M.; Son, J.-Y.; Cui, Y.; Oji, H.; Komaba, S. Impact of the Cut-Off Voltage on Cyclability and Passive Interphase of Sn-Polyacrylate Composite Electrodes for Sodium-Ion Batteries. J. Phys. Chem. C 2016, 120, 15017-15026. (43) Dahbi, M.; Kiso, M.; Kubota, K.; Horiba, T.; Chafik, T.; Hida, K.; Matsuyama, T.; Komaba, S. Synthesis of Hard Carbon from Argan Shells for Na-ion Batteries. J. Mater. Chem. A 2017, 5, 9917-9928. (44) Komaba, S.; Hasegawa, T.; Dahbi, M.; Kubota, K. Potassium Intercalation into Graphite to Realize High-voltage/High-power Potassium-ion Batteries and Potassium-ion Capacitors. Electrochem. Commun. 2015, 60, 172-175. (45) Chou, S.-L.; Pan, Y.; Wang, J.-Z.; Liu, H.-K.; Dou, S.-X. Small Things Make a Big Difference: Binder Effects on the Performance of Li and Na Batteries. Phys. Chem. Chem. Phys. 2014, 16, 20347-20359. (46) Kovalenko, I.; Zdyrko, B.; Magasinski, A.; Hertzberg, B.; Milicev, Z.; Burtovyy, R.; Luzinov, I.; Yushin, G. A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries. Science 2011, 334, 75-79.
29 ACS Paragon Plus Environment
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Poly-ɤ-glutamate Binder to Enhance Electrode Performances of P2-Na2/3Ni1/3Mn2/3O2 for Na-ion Batteries
For Table of Contents Only
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CH2OR H CH2
CF2
n
O O
O
H OR
H
H
OR
NH
H
n
O
Na+
O
R=H, or CH2COONa PVdF
CMCNa Figure 1. Molecular structures of PVdF, CMCNa, and PGluNa.
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PGluNa
n
104
116 110 112
(b)
103
1/6 2/3 1/3 1/6 2/3 2/3 004 100 101 102
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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002
ACS Applied Materials & Interfaces
(a)
10
20
30
40
50
60
70
2deg.(CuK) Figure 2. (a) X-ray diffraction patterns of as-synthesized P2Na2/3Ni1/3Mn2/3O2 and (b) P2-Na2/3Ni1/3Mn2/3O2 immersed in water for one year.
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20th10th
(b) 5.0 4.5 Voltage / V
4.0 3.5 3.0 2.5 2.0
th
th
20 10 0
(d)
1st
50
100
150
3.5 3.0 2.5
160 140 120 100 80
PVdF CMCNa PGluNa
60 40 20
50
100
150
Capacity / mAh g-1
20
30
Cycle number / -
40
50
20th 10th
3.5 3.0 2.5
200
1st
20th 10th 0
50
100
150
200
Capacity / mAh g-1
(f)
100
1st
4.0
1.5
98
200
C / 20 C / 10
C/5
C / 20
2C
1C
180 160
96 94 92 90
PVdF CMCNa PGluNa
88 86
140 120 100 80 60
PVdF CMCNa PGluNa
40
84
20
82 10
PGluNa
2.0
1st
20th10th 0
(e)
180
0
4.0
200
200
(c) 5.0 4.5
1st
20th 10th
2.0
1st
Capacity / mAh g-1
CMCNa
Voltage / V
PVdF
Coulombic efficiency / %
Voltage / V
(a)4.5
Capacity / mAh 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
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Capacity / mAh g-1
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0
10
20
30
40
Cycle number / -
50
0
5
10
15
20
25
Cycle number / -
Figure 3. Charge and discharge curves of (a) PVdF, (b) CMCNa, and (c) PGluNa electrodes in Na cells at a rate of C/20. (d) Capacity retention, (e) Coulombic efficiency, and (f) rate capability of PVdF, CMCNa, and PGluNa electrodes.
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30
ACS Applied Materials & Interfaces
(a)
5.0
PVdF CMCNa PGluNa
4.5
Voltage / V
4.0 3.5 3.0 2.5 2.0 1.5
0
50
100
150
200
Capacity / mAh g-1
(b) 100 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
90
PGluNa
80 70
CMCNa
60
PVdF
50 40 30 20 10 2
3
4
5
6
7
8
9
Cycle number / -
Figure 4. Self-discharge test carried by 10-day storage of fully charged P2NiMN//Na cells up to 4.5 V of 5th charge. (a) Charge and discharge curves of PVdF, CMCNa, and PGluNa electrodes at 5th cycle, in which the cell was stored under open circuit condition for 10 days between 5th galvanostatic chare and discharge and (b) Coulombic efficiency variation of PVdF, CMCNa, and PGluNa electrodes inserting 10-day storage after 5th charge up to 4.5 V.
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4000
(b)
PVdF
4000
3000
3000
2500
2500
2000
1st 5th 10th 20th 30th
1500
10th 1500 1000
500
500
0
500
1000 1500 2000 2500 3000 3500 4000
0
400
300
200
1st 5th 10th 20th 30th
100
2000
1000
0
PGluNa
3500
-Im(Z) /
3500
-Im(Z) /
(a)
-Im(Z) /
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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5th 1st
0 0
100
20th
200
300
400
Re(Z) /
30th
0
500
1000 1500 2000 2500 3000 3500 4000
Re(Z) /
Re(Z) /
Figure 5. Nyquist plots of P2-NiMn electrodes with (a) PVdF and (b) PGluNa binder in three electrode cells, measured at 3.5 V vs. Na+/Na on discharge.
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(a)
O1s
-COONa
-N-C=O-
2wt.ratio 5wt.ratio 10wt.ratio
540
Na2CO3
Nax(Ni, Mn)O2
535 530 Binding energy / eV
(b) C1s
-CH2- CH2-
525
AB
-N-C-
2wt.ratio 5wt.ratio 10wt.ratio -N-C=O-
Na2CO3
NaOOC-
295
290 285 Binding energy / eV
280
Figure 6. XPS spectra of (a) O 1s and (b) C 1s of as-prepared P2-NiMn electrodes with PGluNa binder of which binder rations are x = 2, 5, and 10 in 8 : 1 : x = P2-NiMn : AB : PGluNa by weight.
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(a) O 1s
-COONa
(b) C 1s
Na2CO3
-N-C=O-
-N-C=O-
(c)
-CH2-CH2-
-N-C-
Mn 2p3/2
NaOOC-CH2-CF2-
Mn 2p1/2
PVdF PGluNa
PVdF PGluNa
535
530
Binding eV Bindengenergy energy/ / eV
525
Mn 2p
AB
Na2CO3
Nax(Ni, Mn)O2
540
-CF2-CH2-
295
PVdF PGluNa
290
285
Binding eV Bindengenergy energy/ / eV
280
665
660
655
650
645
640
635
Binding eV Bindengenergy energy/ / eV
Figure 7. XPS spectra of (a) O 1s, (b) C 1s, and (C) Mn 2p of the pristine P2-NiMn electrodes with PVdF and PGluNa binder before cycles.
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(a) Mn2p
(b) O1s Oxygenated and carbonaceous species
Mn 2p1/2
(c) C1s
Na2CO3
AB Na2CO3
Nax(Ni, Mn)O2
NaxPFyOz
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‐CH2‐CF2‐
10th cycle 1st cycle
Mn 2p3/2 10th cycle
‐CF2‐CH2‐ 10th cycle 1st cycle
st
1 cycle
660
655
650
645
640
635
630
540
Binding energy Bindeng energy/ /eV eV
(d) Mn2p
535
530
525
Binding eV Bindengenergy energy/ / eV
(e) O1s
290
(f) C1s
Na2CO3
285
Binding energy eV Bindeng energy // eV ‐CH2‐CH2- ‐N‐C‐
280
AB
‐N‐C=O‐ Nax(Ni, Mn)O2
Mn 2p1/2
660
655
650
Mn 2p3/2
645
640
Bindengenergy energy/ / eV Binding eV
10th cycle 1st cycle
10th cycle 1st cycle
635
630
540
535
530
525
Binding eV Bindeng energy energy / eV
10th cycle 1st cycle
Na2CO3 ‐NaOOC‐
290
285
Bindingenergy energy/ eV / eV Binding
Figure 8. XPS spectra of (a) Mn 2p, (b) O 1s, and (c) C 1s of P2-NiMn electrodes with PVdF binder and (d) Mn 2p, (e) O 1s, and (f) C 1s of P2-NiMn electrodes with PGluNa binder after 1 (black) and 10 (green) cycles in Na cells.
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280
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(a) PVdF
Pristine
10 cycles
30 cycles
(b) PGluNa
Pristine
10 cycles
30 cycles
Figure 9. TEM images of Na2/3Ni1/3Mn2/3O2 with (a) PVdF, and (b) PGluNa binder at pristine(upper) and after 10 (middle) and 30 cycles(bottom).
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(a)
Al foil Composite layer Double-side tape Metallic plate
(b)
5 4
Load / N cm-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
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PGluNa
3 2 1
PVdF
0 0
50
100
Time / sec.
(c)
Al foil
PVdF
Double-side tape
PGluNa
Composite layer
Al foil
Double-side tape Figure 10. (a) Schematic illustration of 90o peel tests. (b) Results of 90o peel test of the P2-NiMn electrode with PVdF and PGluNa binder formed on Al foil. (c) Photos of PVdF and PGluNa electrodes after the peel test.
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(b)
1 mm
3
30
2
20
1
10
0
0
100
200 300 Time / sec.
400
0 500
(d) F(Horizontal) / N
(c)
PGluNa
Depth / m
PVdF
1 mm
3
30
2
20
1
10
0
0
100
200 300 Time / sec.
400
Depth / m
(a)
F(Horizontal) / N
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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0 500
Figure 11. Photos of cutting blades and the composite electrodes with (a) PVdF and (b) PGluNa binder during slicing the electrodes with SAICAS and the results of horizontal cutting load and corresponding depth for (c) PVdF and (d) PGluNa electrodes.
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50
Electrolyte absorption rate / %
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
40
30
25.5 18
20
10
3.5 0
PVdF
CMCNa
PGluNa
Binder film
Figure 12. Electrolyte absorption rate of PVdF, CMCNa, and PGluNa films containing no P2-NiMn nor AB.
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(a)
(b)
PVdF
P2‐NiMn particle AB PVdF
Decomposition products
PGluNa
PGluNa
After cycles
‐ Continuous electrolyte decomposition ‐ Surface deterioration of P2‐NiMn ‐ Electrical isolation
‐ Surface coverage by binder ‐ Stable SEI ‐ Good electrical contact
Figure 13. Schematic illustrations of P2-NiMn composite electrodes with (a) PVdF and (b) PGluNa binder before and after charge/discharge cycles.
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