LITHIUM-AIR BATTERIES:

WISHFUL THINKING OR REALITY?

Jacob Jorne

Department of Chemical Engineering

University of Rochester

Rochester, New York 14627

USA

Rochester in the summer

Rochester in the winter…

Li-Air Battery • The promise and the reality

• Various types of Li-Air batteries

• Flow Li-Air battery

• Air cathode: ORR and OER

• Li peroxide Li2O2: nonconductive solid

• SEI spontaneous and artificial

• Li metal: dendrites

• Charge discharge asymmetry: low efficiency

• Solvent for Li-air battery

• Current R&D efforts

• Conclusions

Ragone plot

Theoretical and practical energy densities of various types

of rechargeable battery.

Lithium-Air Battery

Major Challenge:

Lithium and air

do not “mix”

Like

oil and vinegar

Lithium-Air Battery

Possible Reactions:

• Lithium peroxide:

2Li + O2 => Li2O2 E0=2.96 V

• Lithium superoxide:

4Li + O2 => 2Li2O E0=2.91 V

Powder X-ray diffraction shows that Li2O2 is

formed during charge and decomposed to

O2+Li++e during discharge.

Zinc Air Battery

Four types of Li-air battery.

Lithium Flow Battery (MIT)

Solid state reduction: ZnO to Zn at RDE

Limiting current for solid state ZnO reduction

-50

-40

-30

-20

-10

0

-700 -500 -300 -100

E (mV)

i (m

A)

Levich plot for ZnO solid state reduction

12

10

8

6

4

2

0

kQ

x 1

016 [(A

/cm

2)/

(part

icle

s/c

m3)]

18161412108

1/2

[(rad/s)1/2

]

Least square fit : a = -6.8 ± 0.8 b = 0.90 ± 0.07

Partially reduced ZnO particles

Nonaqueous: Cathode

Schematic representation of the air cathode and proposed

chemistry at the air cathode.

(A) flooded cathode, (B) dry cathode,

and (C) wetted cathode

Lead Acid Battery

Pb(s)/PbSO4(s)/H2SO4/PbO2(s)/P

b

Its success is due to the

conductive PbO2

98.4% oxygen vacancies

N-type semiconductor Eg~0.2eV

PbO2(s)+HSO4-=PbSO4(s)+H++e-

Hybrid

aqueous Li/air with two cathodes (27)

three and two phase systems in (A) aqueous electrolyte

and (B) non-aqueous electrolyte, respectively.

Oxygen Reduction mechanisms

• Li+ + e- => LiO2 3.00 V

• Li+ + e- + LiO2 => Li2O2 2.96 V

• 2Li+ + e- + Li2O2 => 2Li2O 2.91 V

• 2LiO2 => Li2O2 + O2 (chem. Rxn)

• Oxygen reduction reaction: O2-, O22-, O2-

• Irreversible electrochemical reactions.

• High polarization for oxygen evolution.

Schematic illustration of pore filling during discharge. The

growing Li2O2 layer leads to cathode passivation by electrical isolation

(top right) and pore blocking (bottom right).

Bulk Li2O2 and Li2O.

Li (grey) and O (black).

Crystal structure of Li2O2, illustrated using a 2 ! 2 ! 1

expansion of the unit cell. Large green atoms are lithium, and small red

atoms are oxygen. Polyhedra indicate the trigonal prismatic and

octahedral coordination of the two unique Li sites.

Possible discharge mechanisms for a Li-air cell.

Proposed two-stage recharge mechanism for a Li-air cell.

Li2O2 super cell (4x4x2) doped with 1.6% Si atoms (green)

Li (blue) O (red) to improve conductivity

Conductive facets of Li2O2

The existence of facile pathways for electron transport

along Li2O2 surfaces and the absence of the same in

Li2O may explain observations of electrochemical reversibility

in systems where Li2O2 is the discharge product and the

irreversibility of systems that discharge to Li2O.

electron transport through well-connected Li2O2 particles may not significantly hinder performance in Li−oxygen cells.

Lithium Peroxide Surfaces Are Metallic,

While Lithium Oxide Surfaces Are Not.

Radin et al. JACS 2012

Spontaneous and Artificial SEI

Illustration of differences in SEI formation and evolution on

the surfaces of (a) graphite and (b) metal (Li or Li-alloys).

Reproduced from reference 85

A description of the morphology and failure mechanisms of lithium

electrodes during Li deposition and dissolution, and relevant AFM

images

Li-polymer Dendrites: Minimum elastic

modulus and mechanical strength. Silica

nanoparticles. Monroe, U. Michigan

Schematic operation proposed for the rechargeable

aprotic Li-air battery. During discharge, the spontaneous electrochemical

reaction 2LiþO2fLi2O2 generates a voltage of 2.96 Vat

equilibrium (but practically somewhat less due to overpotentials).

During charge, an applied voltage larger than 2.96 V (∼4 V is

required due to overpotentials) drives the reverse electrochemical

reaction Li2O2 f 2Li þ O2.

A single measured discharge-charge cycle for an aprotic

Li-O2 cell (based on SP carbon) operated at ∼0.1 mA/cm2 current

density.

Solvents for Li-Air Battery

• Carbonate solvents are attacked by

oxygen radicals during discharge leading

to Li2CO3 and lithium alkylcarbonates RO-

(C=O)-o-Li instead of Li2O2.

• Di-Methoxy Ethane (DME): poor cycling.

• Glyme-based electrolyte: tetra (ethylene

glycol dimethyl ether: promising.

• Polymer electrolyte: PEO+ =LiCF3SO3

The interaction of propylene carbonate with lithium ions

(white) and oxygen near a surface of Lithium-peroxide

molecular dynamics calculation of silane-based polyether with a lithium

hexafluorophosphate salt. Kah Chun Lau, ANL.

R&D Efforts • - AIST

• - Argonne National Laboratory (ANL)

• - Fudan University

• - Hanyang University

• - IBM

• - Korea Institute of Energy Research

• - Kyushu University

• - Massachusetts Institute of Technology (MIT)

• - Mie University

• - Newcastle University

• - Pacific Northwest National Laboratory (PNNL)

• - Polyplus Battery Company

• - Samsung Elecronics (Samsung Advanced Institute Technology)

• - Seoul National University

• - Toyota

• - US Army Research Lab.

• - University of Dayton Research Institute

• - University of Rome La Sapienza

• - University of St. Andrews

• - University of Texas at Austin

• - University of Waterloo

• - and many more…

IBM’s Battery 500 Technology

POLYPLUS

• 2Li + 1/2O2 + H2O -> 2LiOH 5,000Wh/kg

• 2Li +O2 -> Li2O2 11,000Wh/Kg

• Use Li protection LiPON solid electrolyte

• Problems: Brittle, cracks.

Schematic of EDF’s rechargeable aqueous Li/air cell.

Reproduced from reference 129.

Cross section of PolyPlus’ aqueous Li/air cell.

Reproduced from reference 84.

Schematic of a sealed test cell used by Zhang et al. for

ambient operation of Li/air. Reproduced from reference 149

Something from Nathing (porosity and vacancy)

Porous oxygen-deficient oxide catalyst for Li-Air Battery

Oh, Nazar et al. Nature Chem. 4, 1004-7 (2012)

Catalyst: Pb2+2[Ru1.6Pb4+

0.4]O6.5

Limiting factors that affect the overall performance of

lithium–oxygen batteries.

Trends in oxygen reduction activity (defi ned in the text) plotted

as a function of the oxygen binding energy

Performance of lab scale aqueous Li-air battery

showing 10 complete discharge/charge cycles with a

potential

gap of ca. 0.3 V. 28

Challenges

Two wrongs do not make it

right… In Math:

(-) X (-) = (+)

But not in Li-Air:

(Li dendrites) X (O2 electrode) ≠ (success)

Why jump to Li-Air ?

• Try first Lithium Ion – Air.

• One “mountain” at a time.

• It is easier to sell a great dream than a

good dream…

Summary • Li-Air could be the ultimate battery.

• However, tremendous materials and engineering hurdles.

• Waiting for MAJOR discoveries.

• Concentrate on materials, solvents, polymers rather than on cell design.

• Solid Li2O2: conductive? Where to store?

• Asymmetric charge-discharge: Low efficiency.

• Major decision: All aprotic vs. hybrid aprotic- water

In the running…

Keep Hope Alive Future wishful thought:

All-Electric cars with 400 miles range

No local CO2 emission, no pollution

The bad news:

Electrochemistry will be out of business...

The good news:

It will take a while…

Thank you.