Fenmenos interfaciales en las

bateras de ion litio y de

litio/azufre

Perla B. Balbuena

Department of Chemical Engineering

Department of Materials Science and Engineering

Texas A&M University

College Station, TX 77843

balbuena@tamu.edu

http://engineering.tamu.edu/chemical/people/pbalbuena

Buenos Aires, Agosto 2015

mailto:balbuena@tamu.eduhttp://engineering.tamu.edu/chemical/people/pbalbuena

Interfacial phenomena

solid

liquidmass transfer

heat transfer

reactions

2

Lithium-ion battery (rechargeable)

3

Lithium-ion battery (rechargeable)

https://corneliya.wordpress.com/2013/01/15/interkalationsbatterien-das-problem/ 4

why batteries?

5

.

Necesitamos almacenar la energa

obtenida

Bateras y supercapacitores son las

soluciones mas convenientes

Renewable energies (solar, wind) are intermittent

Energy can be produced

but it must be stored

6

Where may energy be stored?

Liquid fuels (gasoline, methanol, ethanol)

Gas fuels: Hydrogen (fuel cells)

Hydroelectric dam (potential energy)

Electrochemical cells (batteries:

chemical energy)

7

what is the current status

of battery technology?

Li-ion dominates the marketportable electronic devices

Expensive, relatively low energy density electric vehicles

8

Practical vs. theoretical energy density

M. M. Thackeray et al., Energy Environ. Sci., 2012, 5, 78549

Behavior depends on materials properties

B. J. Landi et al, Energy Environ. Sci., 2009, 2, 638-654 10

Li-S battery

From Prof. Vilas Pol, Purdue U. https://engineering.purdue.edu/ViPER/index.html11

https://engineering.purdue.edu/ViPER/index.html

Advantages

S: very abundant

relatively cheap

much less toxic than current Co-oxides

storage capacity: an order of

magnitude > current cathodes

May reach goal of 500 km for EVs and be useful for renewable energies

12

Li-S battery: cathode

P. G. Bruce et al, Nature Materials, 11, p. 19, (2012) 13

Li-S battery: anode

P. G. Bruce et al, Nature Materials, 11, p. 19, (2012)

. dendrite formation

. interfacial reactions

. safety issues

. insulating Li2S film on surface

14

Challenges

Solid S bad ionic/electronic conductor

Changes in S structure during

charge/discharge (swelling, pulverization)

Intermediate compounds shuttle between

electrodes

Li metal anode issues

Low stability short battery life

15

Interfacial phenomena

solid-liquid interfaces

2

unwanted reactions

16

Otherwise:

electron

transfer from

electrode to

electrolyte

may occur

eVoc < Eg

Electrochemical stability

LUMO

HOMO

Eg

E

cathode anode

Electrolyte/

separator

mc(Li)

ma(Li)

eVoc

Condition:

Materials design is crucial

17

First-principles computational

analyses --

understand and predict complex

phenomena

18

Solid-Electrolyte-Interphase layer

SEI--surface film formed at anode and cathode surfaces

Due to electrolyte

decomposition (reduction

or oxidation)

May protect and stabilize anodes (carbon, Li metal); be unstable (metal-oxide cathodes; silicon anodes)

19

Thickness: from a

few to tens or

hundreds of

dense inorganic layer

(from salt decomposition)

porous organic layer

(from solvent decomposition)

SEI mosaic composition

Verma, Maire, Novak, EC Acta 2010

20

How is the SEI layer formed?

21

EC reductive dissociation

B3PW91/6-311++G(d,p)

In gas phase:

thermodynamically forbidden

Wang, Nakamura, Ue, Balbuena, JACS, 123, 11708-11718, (2001)

In solvent:

1 and 2 e- reductions

are possible

22

Li+(EC) reductive dissociation

Ion-pair intermediate;

e- is transferred to EC

Much easier !!!

Li salts facilitate the reaction

Homolytic

ring opening

Radical anion

23

Termination

reactions

lithium butylene dicarbonate

lithium ethylene dicarbonate

+ C2H2

Another e- transfer

Li-carbide

lithium organic salt

with an ester group

insoluble inorganic

Lithium carbonate24

EC

EC + DEC + LiPF6EC + LiPF6

SEI on carbons for different electrolyte compositions

G. Ramos Sanchez, A. Harutyunyan, P. B. Balbuena, JES, in press

Very different SEI

composition and

product distribution

25

LithiationMany Cycles

Si

LithiationMany Cycles

SEI

Si

Nano Today, Volume 7, Issue 5, October 2012, Pages 414-429, ISSN 1748-0132

The Si electrode (capacity: one order of

magnitude > carbon)

SEI layer formation

26

Voltage range

H

O

OH

LiSi

(100)

(101)

Li13Si4

(010)

Highly lithiatedEarly stages of lithiation

LiSi4 LiSi2

~0.2 V0.8 to~0.4 V

LiSi15

27

Extent of lithiation: Effect on EC reduction mechanisms

Very low lithiationLiSi15

Li over the surface

plane; Si-OE bonds

formed

LiSi2 LiSi4

Li on the surface plane or in the

subsurface: Si-C bonds are formed

Intermediate to high lithiationLi13Si4

1 and 2-e- mech.

can coexist

based on calculated

activation energies

2-e- mech. preferred; at higher lithiation

4 e- mech. observed

CE-O cleavage

Ma and Balbuena

JES, 2014

JM Martinez de la Hoz, K Leung and P B Balbuena, ACS Appl. Mat. and Interfaces, 2013 28

VC reduction on lithiated Si anodesCleavage of C1O2 bond: VC (ads) + 2e

- OC2H2OCO2-

(ads)

a) Li-O interaction

b) Formation of C-Si bond

c) Ring opening (open VC2-)

d) Cleavage of a 2nd C1O2 bond

CO2 formation results from: VC + CO32- OC2H2OCO2

2- + CO2

CO32- is a product of EC decomposition

(alternative mechanism to Ushirogata et al, JACS 2013)

VC products: open VC2-, OC2H2O2-, OC2H2OCO2

2-, CO, CO2

C=C containing species

J. M. Martinez de la Hoz and P. B. Balbuena, PCCP, 16 (32), 17091-17098 (2014)

Allsurfaces

Higher lithiated

+ 2e-+ 2e-

29

Effect of degree of lithiation on additives

very low lithiation

FEC: 2 e- mechanism preferred;

CC-OE and Cc-F bond cleavages:

low/moderate barriers

multi-electron

reactions

on highly lithiated

surfaces

2 e- transfer

to FEC ring opening

C-F bond breaking

OC2H3O-, CO2-, F-

OC2H3-, CO2

2-, F-

OCOC2H2O2-, CO2

2-, H, F-open VC2-

FEC can yield open VC anion

(path III) and therefore all VC-

derived products ,

in addition to other specific FEC

products (paths I, II, and III)

J. M. Martinez de la Hoz and P. B. Balbuena, PCCP, 16, 17091-17098 (2014)

Ma and Balbuena

JES, 2014

30

Effects of electrolyte composition

AIMD simulations of mixtures

of various compositions

Goals: clarify additive and

salt effects in mixtures

Illustration:

mixture 3

15% wt VC

JM Martinez de la Hoz, FA Soto and PB Balbuena, JPCC, 201531

surface structure and

electrolyte chemistry play big roles;

how does the surface chemistry matter?

-native oxides

-artificial coating

SiO2 : lithiation and reactivity

hydroxylated amorphous Si surface33

Lithiation formation energy

-2.25

-1.75

-1.25

-0.75

-0.25

0 0.5 1 1.5 2 2.5 3 3.5 4

Fo

rma

tio

n e

ne

rgy

pe

r S

i [e

V]

x in LixSiO2.48H0.963

E(x) = [E(LixSurface) x E(Limetallic) E(Surface)] / N

Saturation point

34

Structural evolution

x in LixSiO2.48H0.963

x = 0 0.37 0.74 1.11 1.48

1.85 2.22 2.59 2.96 3.33

S. Perez Beltran, G. E. Ramirez-Caballero, and PB Balbuena, JPCC, 2015 35

Lithiation mechanisms in native oxides

Si1

Si2O1

Li1

Li2

Li1

Li2

hydroxylated amorphous film LixSiO2.48H0.97

x = 0.37 x = 1.48 x = 3.33

Si-O broken, Si-Si formed, Li6O complexes formed

Perez-Beltran Ramirez-Caballero & Balbuena, JPCC in press 36

Charge of EC vs.Si-C1 distance

0

1

2

3

4

5

-3

-2.5

-2

-1.5

-1

-0.5

0

0 2000 4000 6000 8000

Si-C

1 d

ista

nce

[]

Ele

ctro

nic

char

ge[e

]

Time [fs]

Totalcharge

O1-Li+ = 2.39

O2-C1 = 1.38

O1-Li+ = 2.02

O2-C1 = 1.75

O1-Li+ = 2.0.6

O2-C1 = 1.65 O1-Li

+ = 2.06 O2-C1 = 3.01

EC(ac) + 2e- O(C2H4)OCO

2-(ads)

Optimized ECmolecule

37

Aluminum alcoxide (alucon) coating

Collaboration with Chunmei Ban (NREL)

film formation, lithiation, reactivity38

Film lithiation

-2.63 eV; -3.15 eV; -3.3 eV

binding to

the film stronger

than to Si

agreement with

experiment:

fast film lithiation39

Electronic conductivity in alucone film

film saturation

once the film is saturated with Li,

it becomes electronically conductive;

SEI reactions observed

Collaboration

with C. Ban (NREL)

Balbuena, Seminario, C.H. Ban et al, ACS Appl. Mater. Inter., 7, 11948, (2015)40

Role of Additives

at very low lithiation

FEC: 2 e- mechanism preferred;

CC-OE and Cc-F bond cleavages:

low/moderate barriers

multi-electron

reactions

on highly lithiated

surfaces

2 e- transfer

to FEC ring opening

C-F bond breaking

OC2H3O-, CO2-, F-

OC2H3-, CO2

2-, F-

OCOC2H2O2-, CO2

2-, H, F-open VC2-

FEC can yield open VC anion

(path III) and therefore all VC-

derived products ,

in addition to other specific FEC

products (paths I, II, and III)

Martinez and Balbuena, PCCP, 2014

Ma and Balbuena JES, 2014;

K. Leung et al JES 2014

41

Carbon anodes: effect of surface area

on irreversible capacity

0

500

1000

1500

2000

2500

3000

0 300 600 900 1200 1500

1st

Lit

hi/

de

lith

iati

on

Ca

pa

city

(mA

h/g

)

BET(m2/g)BET (m2/g)

1st

Lith

iati

on

Del

ith

iati

on

Cap

acit

y (m

Ah

/g)

Delithiation

Lithiation

Irreversible capacity

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0 300 600 900 1200 15001

st C

ou

lom

b E

ffic

ien

cy (

%)

BET(m2/g)BET (m2/g)

1st

Co

ulo

mb

Eff

icie

ncy

(%

)

Experimental data from Honda Research Institute, 2014

42

DFT calculated 1st lithiation

intercalation energy and voltage

c) d)

e) f)a) b)

low surface area

high surface area

Omichi, Ramos Sanchez, Harutyunyan, Balbuena, JES, in press

high surface area carbons: much higher capacity to store Li in the 1st lithiation

43

Irreversible capacity loss

Omichi, Ramos Sanchez, Harutyunyan, Balbuena, JES, in press44

Complexation energies of SEI

fragments to LiSpecies Ecomp Ecomp/Li Ecomp-Li

o Ecomp-Li

o /Li

C6O4H10Li5 -9.30 -1.86 -6.59 -3.30

C7O4H15Li3 -6.17 -2.06 -2.78 -2.78

C2O1H5Li2 -4.35 -2.18 -2.25 -2.25

C4O2H10Li5 -9.30 -1.86 -6.59 -3.30

C2O2H4Li7

-5.81 -2.90

C3O2H5Li4 -4.64 -1.16 -1.46 -1.46

C3O3H4Li2

-6.27 -3.13

CO3Li2

-6.38 -3.19

LiF

-4.63 -4.63

45

Irreversible capacity loss due to SEI

First cycle Second cycle

# C # Li # Li SEI # Li int

G-C 144 104 14 70

Capacity: C6Li4.3 Capacity: C6Li0.83

G-H 144 48 7 0

Capacity: C6Li2 Capacity: C6Li1.7

Table 4. First and second cycle capacity as a function of the functional groups in the edges: G-C is the

highest surface area carbon; G-H is a less-high surface area carbon.

46

Back to Li-S battery

2 Highly interconnected chemistry47

Cathode Reactions

S dissolves in electrolyte,

and reacts with Li

EDS Elemental Mapping of

sulfur (29.85 %-wt)

& carbon (65.83 %-wt)

A. Dysart and V. Pol,

Purdue University, 201448

LiTFSI +

electrolyte

/Li {100}

EC+salt on Li(100)

0 fs 6369 fs

330 K

Anode Reactions

49

LiTFSI + electrolyte /Li {100}Summary and comparison

EC

EC LiTFSI/EC-sideways LiTFSI/EC-upwards

T [K] Total time [ps] EC-red time [ps] EC-red time [ps] EC-red

330 14 8.0 7 6.4 6 4.3 7

400 14 8.0 7 6.1 6 3.9 6

DOL

DOL LiTFSI/DOL-sideways LiTFSI/DOL-upwards

T [K] Total time [ps] DOL-red time [ps] DOL-red time [ps] DOL-red

330 13 15.0 0 7.0 0 4.7 0

400 13 15.0 0 6.8 0 4.6 1

DME

DME LiTFSI/DME-sideways LiTFSI/DME-upwards

T [K] Total time [ps] DME-red time [ps] DME-red time [ps] DME-red

330 9 15.0 0 6.6 5 5.1 0

400 9 15.0 0 7.6 0 5.0 0

Very reactive

Low reactivity

Intermediate reactivity

Salt decomposes

always; however,

lower reactivity

with DOL

Surface reconstruction generates

sites where dendritic growth

may occur

50

Shuttle effect: polysulfide

species migrate to anode

51

Effect of PS species on Li anode

52

Li2S formation

Conclusions

Very rich interfacial chemistry

Li consumed in SEI layer is irreversibly lost

Need to generate a stable interfacial layer

Li-S chemistry: highly interconnected system

Experimental/theoretical interaction essential

AcknowledgementsDOE/EERE DE-EE0006832 and

DE-AC02-05CH11231-Sub 7060634

Honda Research Institute

Special thanks to

supercomputer time from:

Brazos HPC Cluster

Collaborators:

Prof. Jorge Seminario (TAMU)

Prof. Partha Mukherjee (TAMU)

Prof. Vilas Pol (Purdue U)

Dr. Kevin Leung (Sandia Nat. Lab)

Dr. Susan Rempe (Sandia Nat. Lab)

Dr. Chunmei Ban (NREL)

Dr. Avetik Harutyunyan (HRI)

54