Graphite Intercalation with Large Fluoroanions

Graphite Intercalation with Large Fluoroanions

Dept. of Chemistry and Center for Advanced Materials, Oregon State University

Oregon State University 2

Intercalation

http://www.cem.msu.edu/~pinnweb/research-na.htm

Oregon State University 3

Intercalation HostsIon exchange: (fixed charge density)

smectite clay Nax+y[Al2-yMgySi4-xAlxO10(OH)2]

layered double hydroxide [Mg3Al(OH)8]Clmetal phosphorous sulfide K0.4[Mn0.80.2PS3]

Redox reaction: (variable charge density)

metal dichalocogenide Lix[MoS2]

layered oxides Lix[CoO2], Nax[MoO3]

graphite K[C8], [C24]HF2

Oregon State University 4

EnergeticsFor clays – reaction is ion-exchange:Na+ Mont- + N(R)4

+ Cl- (aqu) -> N(R)4+ Mont- + NaCl (aqu)

For graphite – reaction is redox:Cx + A -> Cx

+ A-

ΔHrxn = I (Cx) - Ea (A) - ΔHL

Oregon State University 5

Graphite structure C-C in-plane = 1.42 Å Usually (AB)n hexgonal

stacking Interlayer distance

= 3.354 Å

Source: http://www.ccs.uky.edu/~ernst/

A

B

A

Graphite is a semi-metal, chemically stable, light, strong

Oregon State University 6

Graphite Intercalation

-+

-+

-+

oxidant

This is an acceptor-type GICDonor-type reduces layers and intercalates cations

Oregon State University 7

GIC typesReduction M+Cx

-

 Group 1 except Na  Oxidation Cx

+An-

F, Br3-, O (OH)

BF4-, P BiF6

- , GeF62- to PbF6

2-, MoF6-, NiF6

2-, TaF6-, Re PtF6

-

SO4-, NO3

-, ClO4-, IO3

-, VO43-, CrO4

2-

AlCl4-, GaCl4-,FeCl4-, ZrCl6-,TaCl6-

Oregon State University 8

Staging and dimensions

Ic = di + (n - 1) (3.354 Å)

For fluoro, oxometallates di ≈ 8 A, for chlorometallates di ≈ 9-10 A

Oregon State University 9

Graphite oxidation potentials

H2O oxidation potential vs Hammett acidity

Colored regions show the electrochemical potential for GIC stages.

0.9

1.1

1.3

1.5

1.7

-7 -5 -3 -1 1 3 5

H0

E /

V

stage 1 GIC

stage 2

stage 3

high stage

no intercalation

49% hydrofluoric acidAll GICs are

unstable in ambient atmosphere , they oxidize H2O

Oregon State University 10

GIC special issues Anions must be oxidatively stable Larger anions could give larger

galleries, wider range of chemistry GICs that rapidly decompose in air

or aqueous acid are hard to process further

Oregon State University 11

CxPFOS - preparationCx+ K2Mn(IV)F6 + KSO3C8F17

CxSO3C8F17 + K3Mn(III)F6

(CxPFOS)

Solvent = aqueous HF3.35 A

Oregon State University 12

CxPFOS intercalate structure

Anions self-assemble as bilayers within graphite galleries

Oregon State University 13

PFOS twist angle Chain twist

defined by FC-CF tortion

angle

Oregon State University 14

CxPFOS thermal stability

0

20

40

60

80

100

0 200 400 600

temp / °C

mas

s pe

rcen

t

-2.0

-1.0

0.0

1.0

2.0

pow

er /

mW

0

20

40

60

80

100

0 200 400 600

temp / °C

-1.0

2.0

5.0

8.0

11.0

14.0

KPFOSCxPFOS

New syntheses: chemical method

N SO

OCF3S

O

OF3C ..

Cx + K2MnF6 + LiN(SO2CF3)2 CxN(SO2CF3)2 + K2LiMnF6oxidant anion source GIC

1,2

1. 48% hydrofluoric acid, ambient conditions2. hexane, air dry

Oxidant and anion source are separate and changeable. Surprising stability in 50% aqueous acid.

Oregon State University 16

CxN(SO2CF3)2 chem prepn

5 15 25 35 45 55

2 / deg

Inte

n / a

rb u

nits

15 sec

1 min

2 min

4 min

8 min

12 min

15 min

4 wks

graphite

0

20

40

60

80

100

120

0.1 1 10 100 1000 10000reaction time (h)

x

New syntheses: N(SO2CF3)2 orientation

F

F

F

F

Oregon State University 18

CxN(SO2CF3)2 echem prepn

2.0

3.0

4.0

5.0

6.0

0 100 200 300 400 500 600

Capacity (mAh/g)

V v

s Li

+ /Li

charge discharge

ab c

d e

100

4.30 4.70 5.10V vs Li+/Li

dQ/d

V

2 13 2

Oregon State University 19

CxN(SO2CF3)2 - echem prepn

4.0

4.5

5.0

5.5

6.0

0 100 200 300 400

Charge (mAh/g)

V vs

Li+ /L

i

(a)(b)

a

b c

d eb

dCxPFOS

CxN(SO2CF3)2

Oregon State University 20

CxN(SO2CF3)2 anion orientation

Oregon State University 21

CxN(SO2CF3)2 thermal stability

0

20

40

60

80

100

0 200 400 600 800

t / °C

Mas

s lo

ss /

pct (a)(b)

(d)

(e)

(c)

LiN(SO2CF3)2

Oregon State University 22

Imide (NR2-) intercalates

Anion MW di / Å

N(SO2CF3)2 280 8.1

N(SO2C2F5)2 380 8.2

N(SO2CF3) 430 8.3

(SO2C4F9)

Oregon State University 23

Other intercalated anionsAnion MW di / Å

C(SO2CF3)3 411 12.3

SO3C8F17 499 29.5

SO3C10F21 599 33.7

SO3C6F10(C2F5) 461 24.4

1.12

0.78 nm

CxB(O2C2O(CF3)2)2

Stage 2

1.13

0.85 nm

Stage 1

CxB(O2C2(CF3)4)2

Borate chelate GIC’s

Blue: obsPink: calc

Unexpected anion orientation - long axis to sheets

T

Oregon State University 25

Intercalation rates   Intercalate Temp / °C Reaction Anion  half-life / h

SO3C8F17 20 10N(SO2CF3)2 20 0.01N(SO2CF3)(SO2C4F9) 70 100N(SO2CF2CF3)2 70 500C(SO2CF3)3 70 > 1000 SO3C6F5 20, 70 no reaction 

Oregon State University 26

GIC ambient stabilities

0.0

0.1

0.2

0.3

0.4

0.5

0.01 1 100 10000time / h

1 / n

'

TFMI

PFOS

PFEI

nitrate (HF)

sulfate (HF)

bifluoride

stage2

345610

Oregon State University 27

Application - IRP strategy

1. Intercalation2. Removal3. Optional cycle

Targets1. increase internal volume and disorder not surface

area2. low residual content

Parameters: intercalate anion, reduction method (thermolysis, hydrolysis, hydrogenation)

Oregon State University 28

IRP charge-discharge

• GIC is CxPFOS stage 2

• removal is by

heating under N2 for 3 h

• rate = C / 20

irrev reversible

Oregon State University 29

IRP for Li ion battery anodes

0

100

200

300

400

500

600

0 200 400 600 800 1000

temp / °C

capa

city

, mA

h/g

NG, rev

NG, irrev

rev. after IRP

irrev. after IRP

e- + Cx + Li+ = CxLi