Supporting Information

Cryptomelane K1.33Mn8O16 as a Cathode for Rechargeable Aqueous Zinc-ion Batteries

Krishnakanth Sada, Baskar Senthilkumar and Prabeer Barpanda*

Faraday Materials Laboratory, Materials Research Centre, Indian Institute of Science,

Bangalore, 560012, India

* prabeer@.iisc.ac.in, Phone: +91-08-2293-2783; Fax No: +91-80-2360-7316

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019

Crystallographic information

Lattice parameters from the Rietveld refinement of the K1.33Mn8O16 (I4/m space group)

a = 9.8633(11) Å

c = 2.86514(28) Å

Volume = 278.73(8) Å3

Symmetry = Tetragonal

Symmetry space group name H-M = "I4/m"

Table S1: Atomic positions of the K1.33Mn8O16.

Atoms x y z Occ. Uiso Wykoff position

K1 0.0 0.0 0.41979 0.38431 0.06907 4e

Mn1 0.35006 0.16685 0.0 0.96531 0.00139 8h

O1 0.15444 0.20391 0.0 1.00045 0.01327 8h

O2 0.54298 0.16692 0.0 0.91304 0.03215 8h

Table S2: The area ratio of peaks Mn 2p3/2 and 2p1/2.

S.No Area Ratio2p1/2 272.41 Pristine2p3/2 535.7

1.96

2p1/2 381.72 1st discharge2p3/2 796.7

2.08

2p1/2 1068.03 1st charge2p3/2 2130.3

1.99

2p1/2 1450.04 15th discharge2p3/2 2797.0

1.92

Table S3: Comparison of the peak positions at (2θ = 12.9 and 18.2) showing shift in the ratio.

Peak-Position (2θ)

d-spacing(Å)

Counts Ratio

1st charge 12.96 6.80 363718.26 4.85 3694 0.985

1st discharge 12.76 6.93 440218.48 4.79 2026 2.172

15th charge 12.95 6.82 304518.24 4.83 3250 0.9369

15th discharge 12.52 7.06 676818.26 4.85 2809 2.409

Table S4: Comparison of prominent studies on α -MnO2 cathode still date.

Sl. No

Active Material

Discharge product

Morphology Electrolyte Capacity (mA h g-1)

Reference

1 α-MnO2 ZnSO4[Zn(OH2)3]. xH2O, MnOOH

Nanofibers ZnSO4 and MnSO4

(C/5)285

1

2 α-MnO2 ZnMn2O4 and MnOOH

MnO2 deposited on

CFP

ZnSO4 and MnSO4

(0.3C)290

2

3 α-MnO2 ZnMn2O4 Powder ZnSO4 or Zn(NO3)2

(0.5C)210

3

4 α-MnO2 Zn- birnessite Nanorods 1M ZnSO4 (C/20)205

4

5 α-MnO2 ZnMn2O4 Nanorods ZnSO4 233 5

6 KMn8O16 ZnK1-xMn8O16 Nanorods ZnSO4 and K2SO4

(1C) 77 6

7 K1.33Mn8O16 Zn- birnessite Nano particles

ZnSO4 and

MnSO4

(C/10)312

This work

Figure S1: EDS and elemental mapping of the K1.33Mn8O16 showing uniform distribution of constituent elements.

Mn

K

K

Mn

MnO

0 2 4 6 8 10 12 14 16 18 20keVFull Scale 1211 cts Cursor: 2.886 (23 cts)

Spectrum 2

6 µm

6 µm

6 µm 6 µm

K Mn O

Element Weight% Atomic%

O K 42.44 70.73K K 6.73 4.59Mn K 50.83 24.68

Figure S1: EDS and elemental mapping of the K1.33Mn8O16 showing uniform distribution of constituent elements.

Zn-Metal

K0.16MnO2

2M K2SO4

(+)

(-)

1st20th

0 2 4 6 8 10 12 14 16 18

1.0

1.2

1.4

1.6

1.8

Pote

ntia

l (V

)

Capacity (mA h g-1)

C/10

Figure S2: Galvanostatic charge/ discharge (GCD) cycles of K1.33Mn8O16 in 2M K2SO4 electrolyte. (Inset) Schematic presentation of the cell assembly.

0 2 4 6 8

1.0

1.2

1.4

1.6

1.8

Pote

ntia

l (V

vs.

Zn2+

/Zn)

Capacity (mA h g-1)

1st5th10th

Zn-Metal2M ZnSO4/

0.1M MnSO4

(+)

(-)

Carbon Paper

Figure S3: Galvanostatic charge/ discharge (GCD) cycles of carbon paper without active material in 2M ZnSO4 in 0.1M MnSO4 additive electrolyte. (Inset) Schematic presentation of the cell assembly.

1.0 1.2 1.4 1.6 1.8-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1st

2nd

3rd to 5th

Cur

rent

(mA

)

Potential (V vs. Zn2+/Zn)

Scan rate: 0.1 mV/s1.15

V

Figure S4: Cyclic voltammetry (CV) curves recorded in the potential window of 1-1.8 V at a scan rate of 0.1 mV/s.

0 20 40 60 80 100 1200

40

80

120

160

200

240

280

Cycle number

Cap

acity

(mA

h g

-1)

0

20

40

60

80

100

Cou

lom

bic

effic

ienc

y (%

)

Coulombic efficiency (%)Capacity (mA h g-1)

C/2

Figure S5: Cycling stability for 130 cycles at the current rate of C/2.

K1.33Mn8O16Coated on the Carbon paper

Separator Whatman filter paper

Zn metal

Cathode (+) Anode (-)K1.33Mn8O16

Zn-ion Battery

Figure S6: The pouch cell components and different stages of the assembly. The OCV of the two cell is 2.71 V. The assembled pouch cell was tested successfully to light a red LED.

0 50 100 150 200 250 300

1.0

1.2

1.4

1.6

1.8

Poten

tial (V

vs. Z

n2+/Z

n)

Capacity (mA h g-1)

10 15 20 25 30 35 40 45 50 55

2 (degree)

Inte

nsity

(a.u

)

Pristine

Dis 1.42 V

Dis 1.3 V

Dis 1.26 V

Discharge 1V

Char 1.51 V

Char 1.58 V

Charge 1.8 V

** *

* Zn-Birnessite

Figure S7: Ex situ XRD patterns of pristine cathode at different states of charge/discharge. During discharge and charge segments, structural transition (phase transformation) occurred after 1.26 V and 1.51 V respectively.

Figure S7: Comparative EDS spectra of pristine, 1st discharge and 1st charge electrodes.

MnK

KMn

C

MnO

0 2 4 6 8 10 12 14 16 18 20keVFull Scale 743 cts Cursor: 13.091 (0 cts)

Sum Spectrum

MnS K Mn

ZnF

K

Mn

CO

0 2 4 6 8 10 12 14 16 18 20keVFull Scale 980 cts Cursor: 13.091 (0 cts)

Sum Spectrum

MnS K MnSi

KF

Mn

Zn

C

O

0 2 4 6 8 10 12 14 16 18 20keVFull Scale 2275 cts Cursor: 12.612 (0 cts)

Sum Spectrum

1st Discharge

Pristine

1st Charge

Figure S8: Comparative EDS spectra of pristine, 1st discharge and 1st charge electrodes.

2 μm

(a)

1 μm

(b)

Figure S9: SEM images of the electrodes after (a) discharge and (b) charge showing the particles integrity. There is no significant morphological change upon battery cycling.

200 nm

200 nm 200 nm

200 nm 200 nm

Zn

KMn

O

Figure S10: TEM analysis of 15th discharged electrode. Energy-dispersive X-ray microanalysis (EDS) and elemental mapping representing the particle showing the presence of the K-ion in the structure and uniform distribution of the all elements in the particles. Further, it confirmed integrity of the particles upon the multiple (dis)charge cycles.

4 μm 4 μm

Zn

4 μm

K

4 μm

Mn

4 μm

O

4 μm

C

Figure S11: Elemental mapping of the discharged electrode.

4 μm 4 μm

Zn

4 μm

K

4 μm

Mn

4 μm

O

4 μm

C

Figure S12: Elemental mapping of the charged electrode.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

-70

-60

-50

-40

-30

-20

-10

0

10

X in K1.33Mn8O16

Cur

rent

den

sity

(mA

g-1)

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.40

Pote

ntia

l (V

vs.

Zn/

Zn2+

)sada

Figure S13: Potentiostatic intermittent titration (PITT) curve during the 1st discharge revealing the phase transformation with signature bell shape curve.

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