Effect of Concentrated Electrolyte on High Voltage Aqueous Sodium-ion - - PowerPoint PPT Presentation

Kosuke Nakamoto, Ayuko Kitajou*, Masato Ito* and Shigeto Okada* (IGSES, Kyushu University, *IMCE, Kyushu University)

Effect of Concentrated Electrolyte on High Voltage Aqueous Sodium-ion Battery

Oct 6. (Thu) A01-0134

Introduction

This study Advantage /disadvantage Aqueous sodium-ion Non-inflammability, Cost, Power Energy density Post LIB Aqueous lithium-ion Sodium-ion Electrolyte Aqueous Organic Solid Commercial Nickel metal hydride Lithium-ion Sodium sulfur

Commercialized secondary batteries and post lithium-ion batteries

Components Lithium-ion Aqueous sodium-ion Electrolyte solvent Organic Water Electrolyte salt LiPF6, LiTFSI Na2SO4, NaClO4 Separator Polypropylene porous Nonwoven fabric Anode current collector Cu Fe Cathode active material Co, Ni Fe, Mn Electrode slurry thickness ~ 100 µm ~ 20,000 µm Primary requirement to the large scale energy storage system is the cost (Wh/$), rather than specific energy density (Wh/kg). Hybrid capacitor (Aquion Energy) Operation voltage ~ 4 V ~ 2 V

Electrode materials for aqueous lithium-ion battery

Very recent aqueous lithium-ion battery with highly concentrated electrolyte realized high voltage operation exceeding 1.23 V theoretical stability window.

• 3
• 2
• 1

1 2 5 4 3 2 1

E (V) vs. Na/Na+ E (V) vs. Li/Li+ E (V) vs. NHE E (V) vs. Ag/AgCl E = 1.23 – 0.059pH O2↑ H2↑ E = – 0.059pH Theoretical stability window

• f water

7 14 pH

LiNi0.5Mn1.5O4 Li4Ti5O12 LiTi2(PO4)3 LiCoO2 TiO2 LiMn2O4

4 3 2 1

• 3
• 2
• 1

1

Extended practical stability window

• f aqueous lithium-ion electrolyte

Mo6S8 Polyimide LiFePO4 VO2 LiV3O8 LiMn2O4 LiNi0.5Mn1.5O4 Mo6S8

Cathode Anode Electrolyte Voltag e /V Discharge capacity /mAh g-1 Ref. LiMn2O4 VO2 5 mol/l LiNO3 aq. 1.5 50 (electrodes) 1 LiNi0.81Co0.19O2 LiV3O8 1 mol/l Li2SO4 aq. 0.9 20 (electrodes) 2 LiMn2O4 LiTi2(PO4)3 1 mol/l Li2SO4 aq. 1.5 40 (electrodes) 3 LiFePO4 LiTi2(PO4)3 1 mol/l Li2SO4 aq. 0.9 55 (electrodes) 4 LiCoO2 Polyimide 5 mol/l LiNO3 aq. 1.1 71 (electrodes) 5 LiMn2O4 Mo6S8 21 mol/kg LiTFSI aq. 2.0 47 (electrodes) 6 LiMn2O4 TiO2 21 mol/kg LiTFSI + 7 mol/kg LiOTf aq. 2.1 48 (electrodes) 7 LiCoO2 Li4Ti5O12 20 mol/kg LiTFSI + 8 mol/kg LiBETI aq. 2.4 55 (electrodes) 8 LiNi0.5Mn1.5O4 3.0 30 (electrodes)

Estimated cost of recent aqueous lithium-ion chemistries is still high.

Aqueous lithium-ion batteries

[1] W. Li, et al., Science, 264 (1994) 1115. [2] J. Köhler, et al., Electrochim. Acta, 46 (2000) 59. [3] J.Y. Luo, et al., Adv. Funct. Mater., 17 (2007) 3877. [4] J. Luo, et al., Nat. Chem., 2 (2010) 76 [5] H. Qin, et al., J. Power Sources, 249 (2014) 367. [6] L. Suo, et al., Science, 350 (2015) 938. [7] L. Suo, et al., Angew. Chemie., 85287 (2016) 7136. [8] Y. Yamada, et al., Nat. Energy, 1 (2016) 16129.

Cathode Anode Electrolyte Voltage /V Discharge capacity /mAh g-1

Ref.

λ-MnO2 Active Carbon 1 mol/l Na2SO4 aq. 1.2 50 (electrolyte)

9

NaVPO4F Polyimide 5 mol/l NaNO3 aq. 1.1 40 (electrodes)

5

Na3V2O(PO4)2F NaTi2(PO4)3 *10 mol/l NaClO4 aq. 1.4 40 (cathode)

10

Na4Mn9O18 NaTi2(PO4)3 1 mol/l Na2SO4 aq. 1.0 100 (anode)

11

Na2FeP2O7 NaTi2(PO4)3 4 mol/l NaClO4 aq. 0.9 48 (cathode)

12

Na2Ni[Fe(CN)6] NaTi2(PO4)3 1 mol/l Na2SO4 aq. 1.3 100 (anode)

13

Na2Cu[Fe(CN)6] NaTi2(PO4)3 1 mol/l Na2SO4 aq. 1.4 102 (anode)

14

NaCr[Mn(CN)6] Na2Mn[Mn(CN)6] *10 mol/l NaClO4 aq. 1.0 28 (electrodes)

15

Na2Co[Fe(CN)6] NaTi2(PO4)3 1 mol/l Na2SO4 aq. 1.6 120 (cathode)

16

NaFe[Fe(CN)6] (Active Carbon) 1 mol/l Na2SO4 aq. (> 1.5) 60 (cathode)

17

We focus on rocking-chair aqueous sodium-ion batteries (not capacitors). Active materials should be low cost & yield high voltage output to maximize the cost performance index.

Aqueous sodium-ion batteries

[9] J.F. Whitacre, et al., J. Power Sources, 213 (2012) 255. [10] P.R. Kumar, et al., Mater. Chem. A, 3 (2015) 6271. [11] W. Wu, et al., J. Electrochem. Soc., 162 (2015) A803. [12] K. Nakamoto, et al., J. Power Sources, 327 (2016) 327. [13] X. Wu, et al., Electrochem. Commun., 31 (2013) 145. [14] X. Wu, et al., ChemSusChem, 7 (2014) 407. [15] M. Pasta, et al., Nat. Commun., 5 (2014) 3007. [16] X. Wu, et al., ChemNanoMat., 1 (2015) 188. [17] X. Wu, et al., Nano Energy, 13 (2015) 117.

*10 M NaClO4 aq. ≒ 17 m NaClO4 aq.

M Ni Cu Co Fe Initial C/D capacity /mAh g-1

74/65 71/59 142/128 102/122

E/V vs. Ag/AgCl

0.5 0.6 0.9 0.4 1.0 0.2 Electrolyte 1 mol/l Na2SO4 aq. 1 mol/l Na2SO4 aq. 1 mol/l Na2SO4 aq. 1 mol/l Na2SO4 aq.

Upper redox

Inactive Inactive [Fe(CN)6]4-/3- Fe2+/3+

Lower redox

[Fe(CN)6]4-/3- [Fe(CN)6]4-/3- Co2+/3+ [Fe(CN)6]4-/3-

Weak point

Low capacity Expensive Low capacity Expensive Expensive Low initial capacity Air-stability

Sodium metal hexacyanoferrates Na2M[Fe(CN)6], M = Ni, Cu, Fe, Co, Mn

0.5 1.0 0.0 E[V] vs. Ag/AgCl After Wu [13] After Wu [14] After Wu [16] After Wu [17]

Na2Mn[Fe(CN)6] is low cost and was reported high voltage operation in non-aqueous electrolyte but has never been realized in aqueous electrolyte.

Capacity [mAh/g] 150 150 150 150 O2↑ Capacity [mAh/g] Capacity [mAh/g] Capacity [mAh/g]

Sodium metal hexacyanoferrates Na2M[Fe(CN)6], M = Ni, Cu, Fe, Co, Mn

M Mn (in Non-aq.) Co (in Aq.) Fe (in Aq.)

Morph.

Property Round particle with defects Cubic without defects Cubic without defects

After Wu [16] After Wu [17]

Na2Mn[Fe(CN)6] is attractive because of 2 redox-active sites. However, the round particles with defects may dissolve and cannot suppress water decomposition in diluted electrolyte.

E [V] vs. Na/Na+

After Song [18]

3.5 4.0 3.0

→Other methods should be considered as suppressing dissolution and water decomposition.

After Song [18] After Wu [16] After Wu [17]

Capacity [mAh/g] Capacity [mAh/g] 0.5 1.0 0.0 0.5 1.0 0.0 E [V] vs. Ag/AgCl O2↑ E [V] vs. Ag/AgCl 150 50 100 150 50 100 50 100 Capacity [mAh/g]

• Approx. saturated

concentration [mol/kg] Cation Weak points Ref. Li+ Na+ Anion Cl- 18 6 Anodic oxidation & gas evolution

• OH-

5 32 Prussian blue decomposition in alkali 19 NO3

• 13

10 Ti based NASICON corrosion 11 SO4

2-

3 2 Low solubility

• N(SO2CF3)2
• 21

9 High cost TFSI- 6 SO2CF3

• 22

9 High cost OTf- 7 N(SO2C2F5)2

• ND

ND High cost BETI- 8 ClO4

• 6

17 Explosive

• Highly concentrated NaClO4 aqueous electrolyte will suppress

dissolution or side reaction and support high voltage operation.

Electrolyte selection for aqueous sodium-ion battery

[6] L. Suo, et al., Science, 350 (2015) 938. [7] L. Suo, et al., Angew. Chemie., 85287 (2016) 7136. [8] Y. Yamada, et al., Nat. Energy, 1 (2016) 16129. [11] W. Wu, et al., J. Electrochem. Soc., 162 (2015) A803. [19] R. Koncki, et al., Anal. Chem., 70 (1998) 2544.

17

Cathode Electrolyte Anode Na2Mn[Fe(CN)6] (NMHCF) 17 mol/kg NaClO4 aq. NaTi2(PO4)3 (NTP)

Experiment

Synthesis of NaxMn[Fe(CN)6]y・zH2O

Stir (in H2O + EtOH) @ RT Na4[Fe(CN)6] aq. Green blue NaxMn[Fe(CN)6]y・zH2O Filter & Wash (H2O + EtOH) NaCl aq. Light green precipitation MnCl2 aq. Vacuum dry @100 ℃ (over night)

[18] J. Song, et al., J. Am. Chem. Soc., 137 (2015) 2658.

Conventional co-precipitation method [18]

Green blue NaxMn[Fe(CN)6]y・zH2O

Morphological & structural properties of NMHCF

(100) (110) (200) (210) (211) (220) (310) (300) Na2MnFe(CN)6 Pm-3m Cubic ICSD #75-4637

2θ/degree Intensity/a. u.

200 nm

NMHCF powder was identified as cubic with Pm-3m diffraction pattern consistent with Na2Mn[Fe(CN)6]. Approx. 200 nm sized round particles not nano-cubes were observed.

XRD SEM Na Mn Fe H2O 1.24 1 0.81 1.28 By ICP-AES & TGA

As-prepared NMHCF

60 50 40 30 20 10

[20] Y. Morimoto, et al., Energies, 8 (2015) 9486.

[20]

Na1.24Mn[Fe(CN)6]0.81·1.28H2O

(AB : Acetylene black, PTFE ： Polytetrafluoroethylene) WE Ti mesh CE Ti mesh WE pellet (~ 2 mg) CE pellet (~ 3 mg) Ion-type cell Na2Mn[Fe(CN)6] + NaTi2(PO4)3 ⇄ Mn[Fe(CN)6] + Na3Ti2(PO4)3

Electrochemical cell

Beaker-type cell

RE Na2MnFe(CN)6//NaTi2(PO4)3 Working electrode (WE) Electrolyte (EL) Reference electrode (RE) Counter electrode (CE) Na2Mn[Fe(CN)6]：AB：PTFE ＝70：25：5 (wt%) 1 or 17 mol/kg NaClO4 aq. Silver-silver chloride (Ag/AgCl) in sat. KCl aq. NaTi2(PO4)3：AB：PTFE ＝70：25：5 (wt%)

EL

Prussian blue analogues [21] Na2Mn[Fe(CN)6] NMHCF Sodium manganese hexacyanoferrate NASICON-type NaTi2(PO4)3 NTP Sodium titanium phosphate [21] T. Tojo, et al., Electrochem. Acta, 207 (2016) 22.

Result & discussion

1 & 17 mol/kg NaClO4 aqueous electrolyte had 1.9 V & 2.7 V practical stability windows,

• respectively. The windows were larger than 1.23 V theoretical stability window of water.

Cyclic voltammetry on Ti current collector & active materials

4 3 2 1 4 3 2 1 Voltage/V vs. Ag/AgCl Voltage/V vs. Na/Na+ Current/mA 0.5

• 0.5

0.0 Current density/A g-1 0.5

• 0.5

0.0

• 2
• 1

1 2

• 2
• 1

1 2

• 2
• 1

1 2

• 2
• 1

1 2 NMHCF NTP NMHCF NTP

1 mol/kg NaClO4 aq. 17 mol/kg NaClO4 aq. 1 mol/kg NaClO4 aq. 17 mol/kg NaClO4 aq.

Theoretical 1.23 V pH = 7

Practical 1.9 V Practical 2.7 V O2 ↑ H2 ↑ H2 ↑ O2 ↑ O2 ↑ H2 ↑

Theoretical 1.23 V pH = 6

Na1.24Mn[Fe(CN)6]0.81·1.28H2O & NaTi2(PO4)3 half cells

17 mol/kg electrolyte suppressed both of O2/H2 evolution and supported the reversible operation. In contrast, 1 mol/kg electrolyte does not allow cycling.

Voltage/V vs. Ag/AgCl Specific capacity/mAh g-1-anode NMHCF Voltage/V vs. Na/Na+ Specific capacity/mAh g-1-anode Specific capacity/mAh g-1-cathode Specific capacity/mAh g-1-cathode NTP NTP NMHCF 4 3 2 1

1.3 V cut 1.2 V cut

1 mol/kg NaClO4 aq. 2.0 mA cm-2 17 mol/kg NaClO4 aq. 2.0 mA cm-2

150 100 50 150 100 50 1st 2nd

• 2
• 1

1 2 400 300 200 100 1st 2nd 150 100 50

40 30 20 10

Ex-situ XRD patterns of NMHCF cathode in charge/discharge process

40 30 20 10

2θ/degree

1.5 1.0 0.5 0.0 300 250 200 150 100 50

• 50

Voltage/V vs. Ag/AgCl Capacity/mAh g-1 2θ/degree

1.5 1.0 0.5 0.0 400 300 200 100

Capacity/mAh g-1 Voltage/V vs. Ag/AgCl

1 mol/kg NaClO4 aq. NMHCF

XRD intensities of NMHCF in 1 mol/kg electrolyte were weakened at higher voltage range, and some small peaks were observed again at 0.2 V indicating some deposition. Intensity/a. u. Intensity/a. u. 0.2 V 0.7 V 1.3 V 1.2 V 0.9 V OCV 0.2 V 0.7 V 1.3 V 0.9 V OCV 0.2 V 0.7 V 1.3 V 1.2 V 0.9 V OCV 0.2 V 0.7 V 1.3 V 0.9 V OCV

Deposition

17 mol/kg NaClO4 aq. NMHCF

NMHCF cathode deterioration in 1 mol/kg NaClO4 (color, pH, metal ion ICP)

1.5 1.0 0.5 0.0 300 250 200 150 100 50

• 50

Voltage/V vs. Ag/AgCl Capacity/mAh g-1 17 mol/kg NaClO4 aq.

1.5 1.0 0.5 0.0 400 300 200 100

Capacity/mAh g-1 Voltage/V vs. Ag/AgCl 1 mol/kg NaClO4 aq.

Voltage/V

• Prep. Ini.

0.9 1.3 0.7 0.2 pH 6 5 5 0.5 0.8 0.8 Prep . Ini. 0.9 1.2 1.3 0.7 0.2 7 6 4 2 2 2 2 Fe/mol% 0.0 0.0 0.0 0.0 0.0 0.0 Mn/mol% 0.0 0.0 0.0 0.0 0.0 0.0 Ti/mol% 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 6.8 28 27 26 15 0.0 7.3 8.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

In 1 mol/kg electrolyte, NMHCF dissolved as [Fe(CN)6]4- at lower, [Fe(CN)6]3- at higher voltage, and MnO precipitating accompanied with Mn2+ dissolution on the cathode and OH- generated on NTP.

[Fe(CN)6]4- dissolution [Fe(CN)6]3- dissolution

MnO precipitation

[Fe(CN)6]α- deposition H3O+ extraction Partially O2↑ [Fe(CN)6]4- dissolution [Fe(CN)6]3- dissolution

MnO precipitation

No dissolution or no precipitation Strong acidic Mild acidic deposition

Deterioration process in 1 mol/kg NaClO4 aq.

Voltage/V vs. Ag/AgCl Specific capacity/mAh g-1-anode NMHCF Voltage/V vs. Na/Na+ Specific capacity/mAh g-1-anode Specific capacity/mAh g-1-cathode Specific capacity/mAh g-1-cathode NTP NTP NMHCF 4 3 2 1

1.3 V cut 1.2 V cut

1 mol/kg NaClO4 aq. 2.0 mA cm-2 17 mol/kg NaClO4 aq. 2.0 mA cm-2

150 100 50 150 100 50 1st 2nd

• 2
• 1

1 2 400 300 200 100 1st 2nd 150 100 50

Deterioration process in 1 mol/kg NaClO4 aq. Water decomposition 2H2O + 2e- → H2↑ + 2OH- Cathode decomposition Na2-xMn[Fe(CN)6] + 2NaOH → Na4-x[Fe(CN)6] + MnO↓ + H2O

2H2O + 2e- → H2↑ + 2OH-

100 50 100 80 60 40 20 100 50 100 80 60 40 20

Electrolyte concentration & rate dependences on cyclability of NMHCF cathode

Better cycle performances of NMHCF cathode were obtained in more concentrated electrolytes and at larger current densities.

Cycle number Discharge capacity/mAh g-1

Fe2+/Fe3+ + Mn2+/Mn3+ Fe2+/Fe3+

Discharge capacity retention/% Cycle number

Concentration dependence at const. 2.0 mA cm-2 Rate dependence in const.17 mol/kg electrolyte

17 mol/kg 14 mol/kg 10 mol/kg 7 mol/kg 1 mol/kg 5.0 mA cm-2 2.0 mA cm-2

Binding energy/eV Binding energy/eV

730 720 710 700

NMHCF cathode operation (structural & metal ion valence changes)

1.5 1.0 0.5 0.0 300 250 200 150 100 50

• 50

Voltage/V vs. Ag/AgCl Capacity/mAh g-1

XPS of Fe XPS of Mn XRD C/D profile of NMHCF in 17 mol/kg NaClO4 aq.

NMHCF cathode worked with Fe2+/Fe3+ redox, partial Mn2+/Mn3+ redox and Na ion extraction/insertion in highly concentrated 17 mol/kg NaClO4 aq.

18 17 16 660 650 640

2θ/degree Calc. valence state

Fe2+ /Mn2+ Fe3+ /Mn2+ Fe3+ /Mn2.43+ Fe3+ /Mn2+ Fe2+ /Mn2+

Calc. Na amount

1.24 0.42 0.42 1.24

monoclinic monoclinic cubic cubic tetragonal

100 50 20 15 10 5 1.0 0.5 0.0 2.5 2.0 1.5 1.0 0.5 0.0 150 100 50 1.5 1.0 0.5 0.0 1st 2nd

x in Na1.24-xMn[Fe(CN)6]0.81·1.28H2O Capacity/mAh g-1–cathode Voltage/V vs. NaTi2(PO4)3 2.0 mA cm-2 0.5 ~ 2.0 V

100 80 60 40 20 50 40 30 20 10 Retention/% Cycle number

Current density/mA cm-2 Discharge capacity/mAh g-1 cathode Cathode: 20 mg cm-2, 200 µm Anode: 30 mg cm-2, 200 µm

High voltage aqueous sodium-ion battery of NMHCF/17 m NaClO4 aq./NTP

Na1.24Mn[Fe(CN)6]0.81/17 mol/kg NaClO4 aq./NaTi2(PO4)3 operates at 1.3, 1.5 & 1.8 V. The cell exhibited initial discharge capacity of 117 mAh g-1, good cycle & rate performances. Current density/A g-1-cathode 0.5 ~ 2.0 V

Conclusions

Conclusion

Electrodes selection Na2MnFe(CN)6 cathode & NaTi2(PO4)3 anode were selected because of high voltage combination and low cost of the materials. Electrolyte selection Low cost NaClO4 salt can realize highly concentrated aqueous electrolyte, which suppresses water decomposition. Effect of concentrated electrolyte Concentrated 17 mol/kg electrolyte suppressed the water decomposition and dissolution of NMHCF cathode compared to diluted 1 mol/kg electrolyte. Factor of cathode deterioration in 1 mol/kg electrolyte Prussian blue analogue cathode was decomposed by hydroxide ion occurred

• n the anode because of the small practical stability window of 1 mol/kg electrolyte.

High voltage aqueous sodium-ion battery Na1.24Mn[Fe(CN)6]0.81/17 mol/kg NaClO4 aq./NaTi2(PO4)3 operates over 1.2 V. The cell delivered initial discharge capacity of 117 mAh g-1, good cycle & rate performances.

Thank you for your attention Acknowledgement This research was financially supported by ESICB,

Elements Strategy Initiative for Catalysts and Batteries

Project, MEXT, Japan.