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

Transcription

1 Effect of Concentrated Electrolyte on High Voltage Aqueous Sodium-ion Battery Kosuke Nakamoto, Ayuko Kitajou*, Masato Ito* and Shigeto Okada* (IGSES, Kyushu University, *IMCE, Kyushu University) Oct 6. (Thu) A1-134

2 Introduction

3 Commercialized secondary batteries and post lithium-ion batteries Electrolyte Aqueous Organic Solid Commercial Nickel metal hydride Lithium-ion Sodium sulfur Post LIB Aqueous lithium-ion Sodium-ion This study Advantage /disadvantage Aqueous sodium-ion Non-inflammability, Cost, Power! Energy density Hybrid capacitor (Aquion Energy) Components Lithium-ion Aqueous sodium-ion Electrolyte solvent Organic Water Electrolyte salt LiPF 6, LiTFSI Na 2 SO 4, NaClO 4 Separator Polypropylene porous Nonwoven fabric Anode current collector Cu Fe Cathode active material Co, Ni Fe, Mn Electrode slurry thickness ~ 1 µm ~ 2, µm Operation voltage ~ 4 V ~ 2 V Primary requirement to the large scale energy storage system is the cost (Wh/$), rather than specific energy density (Wh/kg).

4 Electrode materials for aqueous lithium-ion battery 2 5 LiNi.5 Mn 1.5 O 4 1 E = pH O LiCoO 2 LiMn 2 O 4 LiNi.5 Mn 1.5 O 4 1 E (V) vs. NHE -1 Theoretical stability window of water H 2 E =.59pH 3 2 E (V) vs. Li/Li + E (V) vs. Na/Na LiFePO 4 LiMn 2 O 4 Mo 6 S 8 Polyimide LiV 3 O 8 LiTi 2 (PO 4 ) VO 2 3 Mo 6 S 8 TiO 2-1 E (V) vs. Ag/AgCl ph 1 1 Li 4 Ti 5 O 12 Extended practical stability window of aqueous lithium-ion electrolyte -3 Very recent aqueous lithium-ion battery with highly concentrated electrolyte realized high voltage operation exceeding 1.23 V theoretical stability window. -2

5 Aqueous lithium-ion batteries Cathode Anode Electrolyte Voltag e /V Discharge capacity /mah g -1 LiMn 2 O 4 VO 2 5 mol/l LiNO 3 aq (electrodes) 1 LiNi.81 Co.19 O 2 LiV 3 O 8 1 mol/l Li 2 SO 4 aq..9 2 (electrodes) 2 LiMn 2 O 4 LiTi 2 (PO 4 ) 3 1 mol/l Li 2 SO 4 aq (electrodes) 3 LiFePO 4 LiTi 2 (PO 4 ) 3 1 mol/l Li 2 SO 4 aq (electrodes) 4 LiCoO 2 Polyimide 5 mol/l LiNO 3 aq (electrodes) 5 LiMn 2 O 4 Mo 6 S 8 21 mol/kg LiTFSI aq (electrodes) 6 LiMn 2 O 4 TiO 2 21 mol/kg LiTFSI + 7 mol/kg LiOTf aq. Ref (electrodes) 7 LiCoO 2 2 mol/kg LiTFSI (electrodes) Li 4 Ti 5 O 12 LiNi + 8 mol/kg LiBETI aq..5 Mn 1.5 O (electrodes) 8 Estimated cost of recent aqueous lithium-ion chemistries is still high. [1] W. Li, et al., Science, 264 (1994) [2] J. Köhler, et al., Electrochim. Acta, 46 (2) 59. [3] J.Y. Luo, et al., Adv. Funct. Mater., 17 (27) [4] J. Luo, et al., Nat. Chem., 2 (21) 76 [5] H. Qin, et al., J. Power Sources, 249 (214) 367. [6] L. Suo, et al., Science, 35 (215) 938. [7] L. Suo, et al., Angew. Chemie., (216) [8] Y. Yamada, et al., Nat. Energy, 1 (216)

6 Aqueous sodium-ion batteries *1 M NaClO 4 aq. 17 m NaClO 4 aq. Cathode Anode Electrolyte Voltage /V Discharge capacity /mah g -1 λ-mno 2 Active Carbon 1 mol/l Na 2 SO 4 aq (electrolyte) 9 NaVPO 4 F Polyimide 5 mol/l NaNO 3 aq (electrodes) 5 Na 3 V 2 O(PO 4 ) 2 F NaTi 2 (PO 4 ) 3 *1 mol/l NaClO 4 aq (cathode) 1 Na 4 Mn 9 O 18 NaTi 2 (PO 4 ) 3 1 mol/l Na 2 SO 4 aq (anode) 11 Na 2 FeP 2 O 7 NaTi 2 (PO 4 ) 3 4 mol/l NaClO 4 aq (cathode) 12 Na 2 Ni[Fe(CN) 6 ] NaTi 2 (PO 4 ) 3 1 mol/l Na 2 SO 4 aq (anode) 13 Na 2 Cu[Fe(CN) 6 ] NaTi 2 (PO 4 ) 3 1 mol/l Na 2 SO 4 aq (anode) 14 NaCr[Mn(CN) 6 ] Na 2 Mn[Mn(CN) 6 ] *1 mol/l NaClO 4 aq (electrodes) 15 Na 2 Co[Fe(CN) 6 ] NaTi 2 (PO 4 ) 3 1 mol/l Na 2 SO 4 aq (cathode) 16 NaFe[Fe(CN) 6 ] (Active Carbon) 1 mol/l Na 2 SO 4 aq. (> 1.5) 6 (cathode) 17 Ref. 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. [9] J.F. Whitacre, et al., J. Power Sources, 213 (212) 255. [1] P.R. Kumar, et al., Mater. Chem. A, 3 (215) [11] W. Wu, et al., J. Electrochem. Soc., 162 (215) A83. [12] K. Nakamoto, et al., J. Power Sources, 327 (216) 327. [13] X. Wu, et al., Electrochem. Commun., 31 (213) 145. [14] X. Wu, et al., ChemSusChem, 7 (214) 47. [15] M. Pasta, et al., Nat. Commun., 5 (214) 37. [16] X. Wu, et al., ChemNanoMat., 1 (215) 188. [17] X. Wu, et al., Nano Energy, 13 (215) 117.

7 Sodium metal hexacyanoferrates Na 2 M[Fe(CN) 6 ], M = Ni, Cu, Fe, Co, Mn M Ni Cu Co Fe E[V] vs. Ag/AgCl Initial C/D capacity 74/65 71/59 142/128 12/122 /mah g -1 E/V vs. Ag/AgCl.5.6 Electrolyte 1 mol/l Na 2 SO 4 aq. 1 mol/l Na 2 SO 4 aq. 1 mol/l Na 2 SO 4 aq. 1 mol/l Na 2 SO 4 aq. Upper redox Lower redox Weak point 1..5 After Wu [13] After Wu [14] After Wu [16] After Wu [17]. Capacity [mah/g] 15 Capacity [mah/g] 15 Capacity [mah/g] 15 Capacity [mah/g] 15 Inactive Inactive [Fe(CN) 6 ] 4-/3- Fe 2+/3+ [Fe(CN) 6 ] 4-/3- [Fe(CN) 6 ] 4-/3- Co 2+/3+ [Fe(CN) 6 ] 4-/3- Low capacity Expensive Low capacity Expensive O Expensive Na 2 Mn[Fe(CN) 6 ] is low cost and was reported high voltage operation in non-aqueous electrolyte but has never been realized in aqueous electrolyte Low initial capacity Air-stability

8 Sodium metal hexacyanoferrates Na 2 M[Fe(CN) 6 ], M = Ni, Cu, Fe, Co, Mn M Mn (in Non-aq.) Co (in Aq.) Fe (in Aq.) E [V] vs. Na/Na + After Song [18] E [V] vs. Ag/AgCl O 2 E [V] vs. Ag/AgCl After Wu [16] After Wu [17] Capacity [mah/g] Capacity [mah/g] Capacity [mah/g] After Song [18] After Wu [16] After Wu [17] 15 Morph. Property Round particle with defects Cubic without defects Cubic without defects Na 2 Mn[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. Other methods should be considered as suppressing dissolution and water decomposition.

9 Electrolyte selection for aqueous sodium-ion battery Approx. saturated concentration [mol/kg] Anion Cation Li + Na + Weak points Cl Anodic oxidation & gas evolution - OH Prussian blue decomposition in alkali 19 NO Ti based NASICON corrosion 11 SO Low solubility - N(SO 2 CF 3 ) High cost TFSI - 6 SO 2 CF High cost OTf - 7 N(SO 2 C 2 F 5 ) 2 - ND ND High cost BETI - 8 ClO Explosive - Highly concentrated NaClO 4 aqueous electrolyte will suppress dissolution or side reaction and support high voltage operation. Cathode Electrolyte Anode Na 2 Mn[Fe(CN) 6 ] (NMHCF) 17 mol/kg NaClO 4 aq. NaTi 2 (PO 4 ) 3 (NTP) [6] L. Suo, et al., Science, 35 (215) 938. [7] L. Suo, et al., Angew. Chemie., (216) [8] Y. Yamada, et al., Nat. Energy, 1 (216) [11] W. Wu, et al., J. Electrochem. Soc., 162 (215) A83. [19] R. Koncki, et al., Anal. Chem., 7 (1998) Ref.

10 Experiment

11 Synthesis of Na x Mn[Fe(CN) 6 ] y zh 2 O Conventional co-precipitation method [18] Na 4 [Fe(CN) 6 ] aq. NaCl aq. Stir (in H 2 O + RT MnCl 2 aq. Filter & Wash (H 2 O + EtOH) Light green precipitation Vacuum (over night) Green blue Na x Mn[Fe(CN) 6 ] y zh 2 O Green blue Na x Mn[Fe(CN) 6 ] y zh 2 O [18] J. Song, et al., J. Am. Chem. Soc., 137 (215) 2658.

12 Morphological & structural properties of NMHCF XRD As-prepared NMHCF SEM Intensity/a. u. 1 [2] (1) (11) 2 3 (2) (21) (211) 4 2θ/degree Na 2 MnFe(CN) 6 Pm-3m Cubic ICSD # (22) (3) (31) nm By ICP-AES & TGA Na Mn Fe H 2 O NMHCF powder was identified as cubic with Pm-3m diffraction pattern consistent with Na 2 Mn[Fe(CN) 6 ]. Approx. 2 nm sized round particles not nano-cubes were observed. [2] Y. Morimoto, et al., Energies, 8 (215) Na 1.24 Mn[Fe(CN) 6 ] H 2 O

13 Electrochemical cell (AB : Acetylene black, PTFE : Polytetrafluoroethylene) Working electrode (WE) Electrolyte (EL) Reference electrode (RE) Counter electrode (CE) Na 2 Mn[Fe(CN) 6 ]:AB:PTFE =7:25:5 (wt%) 1 or 17 mol/kg NaClO 4 aq. Silver-silver chloride (Ag/AgCl) in sat. KCl aq. NaTi 2 (PO 4 ) 3 :AB:PTFE =7:25:5 (wt%) RE WE Ti mesh CE Ti mesh Prussian blue analogues [21] Na 2 Mn[Fe(CN) 6 ] NMHCF Sodium manganese hexacyanoferrate WE pellet (~ 2 mg) EL Beaker-type cell CE pellet (~ 3 mg) NASICON-type NaTi 2 (PO 4 ) 3 NTP Sodium titanium phosphate Na 2 MnFe(CN) 6 //NaTi 2 (PO 4 ) 3 Ion-type cell Na 2 Mn[Fe(CN) 6 ] + NaTi 2 (PO 4 ) 3 Mn[Fe(CN) 6 ] + Na 3 Ti 2 (PO 4 ) 3 [21] T. Tojo, et al., Electrochem. Acta, 27 (216) 22.

14 Result & discussion

15 Cyclic voltammetry on Ti current collector & active materials Current density/a g -1 Current/mA mol/kg NaClO 4 aq. 1 mol/kg NaClO 4 aq. H 2 H 2 NTP 3 Practical 1.9 V Theoretical 1.23 V ph = 7 NMHCF Voltage/V vs. Na/Na mol/kg NaClO 4 aq. O Practical V O 2 H 2 Theoretical 1.23 V ph = 6 O 2 NTP 3 17 mol/kg NaClO 4 aq. 4 NMHCF Voltage/V vs. Ag/AgCl & 17 mol/kg NaClO 4 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.

16 Na 1.24 Mn[Fe(CN) 6 ] H 2 O & NaTi 2 (PO 4 ) 3 half cells Voltage/V vs. Ag/AgCl Specific capacity/mah g -1 -cathode NMHCF NTP V cut V cut 5 1 Specific capacity/mah g -1 -anode 1st 2nd 4 NTP Specific capacity/mah g -1 -cathode NMHCF 4 1 mol/kg NaClO 4 aq. 17 mol/kg NaClO 4 aq. 2. ma cm ma cm Specific capacity/mah g -1 -anode 1st 2nd Voltage/V vs. Na/Na + 17 mol/kg electrolyte suppressed both of O 2 /H 2 evolution and supported the reversible operation. In contrast, 1 mol/kg electrolyte does not allow cycling.

17 Ex-situ XRD patterns of NMHCF cathode in charge/discharge process Capacity/mAh g mol/kg NaClO 4 aq. NMHCF 1.3 V.7 V 1.2 V.9 V.2 V OCV Intensity/a. u. Deposition.2 V.7 V 1.3 V 1.2 V.9 V OCV Capacity/mAh g mol/kg NaClO 4 aq. NMHCF.7 V 1.3 V.9 V.2 V OCV Intensity/a. u..2 V.7 V 1.3 V.9 V OCV Voltage/V vs. Ag/AgCl θ/degree Voltage/V vs. Ag/AgCl θ/degree 4 XRD intensities of NMHCF in 1 mol/kg electrolyte were weakened at higher voltage range, and some small peaks were observed again at.2 V indicating some deposition.

18 NMHCF cathode deterioration in 1 mol/kg NaClO 4 (color, ph, metal ion ICP) Capacity/mAh g -1 Capacity/mAh g -1 Voltage/V vs. Ag/AgCl Prep. [Fe(CN) 6 ] 4- dissolution [Fe(CN) 6 ] 3- dissolution 1 mol/kg NaClO 4 aq. MnO precipitation 4 [Fe(CN) 6 ] α- deposition Voltage/V vs. Ag/AgCl mol/kg NaClO 4 aq. H 3 O + extraction Partially O 2 Voltage/V Prep. Ini Ini ph [Fe(CN) ] 4- Mild acidic Strong acidic dissolution [Fe(CN) 6 ] 3- dissolution deposition 25 3 MnO precipitation No dissolution or no precipitation Fe/mol% Mn/mol% Ti/mol% 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 Mn 2+ dissolution on the cathode and OH - generated on NTP.

19 Deterioration process in 1 mol/kg NaClO 4 aq. Voltage/V vs. Ag/AgCl Specific capacity/mah g -1 -cathode NMHCF NTP V cut V cut 5 1 Specific capacity/mah g -1 -anode 1st 2nd 2H 2 O + 2e - H 2 + 2OH - 4 NTP Specific capacity/mah g -1 -cathode NMHCF 4 1 mol/kg NaClO 4 aq. 17 mol/kg NaClO 4 aq. 2. ma cm ma cm Specific capacity/mah g -1 -anode 1st 2nd Voltage/V vs. Na/Na + Deterioration process in 1 mol/kg NaClO 4 aq. Water decomposition 2H 2 O + 2e - H 2 + 2OH - Cathode decomposition Na 2-x Mn[Fe(CN) 6 ] + 2NaOH Na 4-x [Fe(CN) 6 ] + MnO + H 2 O

20 Electrolyte concentration & rate dependences on cyclability of NMHCF cathode Concentration dependence at const. 2. ma cm -2 Rate dependence in const.17 mol/kg electrolyte Discharge capacity/mah g Fe 2+ /Fe 3+ + Mn 2+ /Mn mol/kg 14 mol/kg 1 mol/kg Fe 2+ /Fe 3+ 7 mol/kg 1 mol/kg Discharge capacity retention/% ma cm ma cm Cycle number Cycle number Better cycle performances of NMHCF cathode were obtained in more concentrated electrolytes and at larger current densities.

21 NMHCF cathode operation (structural & metal ion valence changes) C/D profile of NMHCF in 17 mol/kg NaClO 4 aq. 3 Calc. Calc. XPS of Fe valence XPS of Mn Na XRD state amount 25 Fe 2+ /Mn monoclinic Capacity/mAh g Fe 3+ /Mn 2+ Fe 3+ /Mn Fe 3+ /Mn cubic tetragonal cubic Voltage/V vs. Ag/AgCl Binding energy/ev Fe 2+ /Mn Binding energy/ev monoclinic 17 2θ/degree 18 NMHCF cathode worked with Fe 2+ /Fe 3+ redox, partial Mn 2+ /Mn 3+ redox and Na ion extraction/insertion in highly concentrated 17 mol/kg NaClO 4 aq.

22 High voltage aqueous sodium-ion battery of NMHCF/17 m NaClO 4 aq./ntp Voltage/V vs. NaTi 2 (PO 4 ) x in Na 1.24-x Mn[Fe(CN) 6 ] H 2 O.5 2. ma cm -2.5 ~ 2. V 5 Retention/% Capacity/mAh g -1 cathode 1.5 1st 2nd Cycle number 15 Discharge capacity/mah g -1 cathode 1. 5 Current density/a g -1 -cathode 5.5 Cathode: 2 mg cm -2, 2 µm Anode: 3 mg cm -2, 2 µm 1 15 Current density/ma cm ~ 2. V 2 Na 1.24 Mn[Fe(CN) 6 ].81 /17 mol/kg NaClO 4 aq./nati 2 (PO 4 ) 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.

23 Conclusions

24 Conclusion Electrodes selection Na 2 MnFe(CN) 6 cathode & NaTi 2 (PO 4 ) 3 anode were selected because of high voltage combination and low cost of the materials. Electrolyte selection Low cost NaClO 4 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 on the anode because of the small practical stability window of 1 mol/kg electrolyte. High voltage aqueous sodium-ion battery Na 1.24 Mn[Fe(CN) 6 ].81 /17 mol/kg NaClO 4 aq./nati 2 (PO 4 ) 3 operates over 1.2 V. The cell delivered initial discharge capacity of 117 mah g -1, good cycle & rate performances.

25 Acknowledgement This research was financially supported by ESICB, Elements Strategy Initiative for Catalysts and Batteries Project, MEXT, Japan. Thank you for your attention