Introduction

Motivation for Li-O2 Batteries:• The electrification of transportation would decrease the consumption of fossil fuels,

reducing CO2 emissions and dependence on foreign oil imports• Li-ion is currently the most widely used rechargeable battery in electric vehicles• Li-ion is limited by an inadequate specific energy density • The Li-O2 battery has a potentially much higher specific energy density

Motivation for project:• Electrolyte selection is a critical barrier preventing the Li-O2 battery from commercial

viability • Decomposition reactions involving the electrolyte during discharge and charge limit

cycling of the battery, and high overpotentials limit the cycling efficiency• LiNO3 salt in N,N-dimethylacetamide (DMA) solvent is a promising electrolyte because

of its stability at 1 M concentration• Preliminary results for higher [LiNO3] in DMA show greater stability during cycling and

larger cell capacity

Results (cont.)

Charles T. Wan1, Colin M. Burke2, & Bryan D. McCloskey2, PhD.1Cornell University, Ithaca, NY. 2University of California, Berkeley, Berkeley, CA

Examining the Performance of the Electrolyte LiNO3

in N,N-Dimethylacetamide in Li-O2 Batteries

Electrolyte (e-/O2)dis (e-/O2)chg OER/ORR

1 M LiNO3 DMA 2.06 2.67 0.77

3 M LiNO3 DMA 2.09 2.51 0.83

5 M LiNO3 DMA 2.03 2.46 0.82

References•Burke, C., Pande V., Khetan A., Viswanathan V., and McCloskey B. PNAS. 2015, 30, 9293-9298.

•Girishkumar, G.; McCloskey, B. et al. J. Phys. Chem. Lett. 2010, 1, 2193-2203.

•McCloskey, B. D. et al. J. Phys. Chem. Lett. 2013, 4, 2989- 2993.

•Walker, W., Giordani, V., et.al. J. Phys. Chem. Lett. 2013, 135, 2076-2079

Acknowledgements

Conclusion

• There exists a positive correlation between capacity and [LiNO3] in DMA• SEM images show Li2O2 toroid formation at higher [LiNO3]. This indicates that a

solution-mediated mechanism is taking place, which could explain enhanced capacity• NMR measurements suggest Li+ solvation does not vary over the [LiNO3] range,

contradicting toroid evidence of [LiNO3] dependence• Pressure decay/rise experiments and titration yields point toward increased cycling

stability as [LiNO3] nears the saturation point in the electrolyte

Methods and Materials

Electrochemical tests to determine stability of electrolyte and cell capacity were conducted on custom Swagelok batteries (see right).

𝐋𝐢𝟐𝐎𝟐 + H2SO4 → 𝐇𝟐𝐎𝟐 + 2Li+ + SO42− (1)

𝐇𝟐𝐎𝟐 + 2KI + H2SO4 → 𝐈𝟐 + K2SO4 + 2H2O (2)𝐈𝟐 + 𝟐𝐍𝐚𝟐𝐒𝟐𝐎𝟑 → Na2S4O6 + 2NaI (3)

Iodometric titrations to determine Li2O2 yield after discharge follow a similar

procedure as described previously. The reactions take place as shown below:

Quantitative analysis of O2

consumed and evolved wasgathered on this equipment,which samples and quantifiesgas evolved in real time.

Battery cell design:

Custom-built differential electrochemical mass spectrometer:

This work was funded by the Amgen Scholars program. I would like to thank Professor McCloskey and the McCloskey lab for this research opportunity. I would also like to acknowledge Colin Burke for his excellent mentorship and guidance throughout this experience. Many thanks to Jessica Nichols and the rest of the lab for their advice and support as well.

Improvement in cycling stability with increasing [LiNO3]:

Galvanostatic discharge/charge profiles with corresponding pressure decay/rise graphs for Li-

O2 batteries (250 µA cycle for 1 M and 5 M, 250 µA discharge and 100 µA charge for 3 M). The

chart is a summary of Faradaic charge compared to moles of O2 consumed and evolved for

discharge and charge, respectively.

Results

Cells were discharged at 250 µA in ~1.5 atm O2 atmosphere for 1mAh. Scale bars all 1 µm. Insets are to make Li2O2 toroids easier to see.

Representative galvanostatic discharge profiles for Li-O2 batteries (250 µA in ~1.5 atm

O2 atmosphere until 2V cutoff).

Preliminary data shows an increase in cell capacity with higher [LiNO3] :

Scanning Electron Microscopy (SEM) images of discharged cathodes show toroid formation at higher [LiNO3]:

1 M LiNO3 DMA 5 M LiNO3 DMA3 M LiNO3 DMA

Li+ solvation not affected by salt concentration:

Low Li2O2 titration yields:

7Li Nuclear Magnetic Resonance (NMR) spectroscopy of electrolytes versus a 3 M LiCl in D2O reference show no significant change in chemical shift as a function of [LiNO3]. The 7Li chemical shift can be correlated to LiO2

intermediate solvation, which in turn is related to toroid formation.

Titrated cells were discharged at 250 µAin ~1.5 atm O2 atmosphere for 1 mAh.Titrations reveal information aboutpossible parasitic chemistry duringdischarge.

00.20.40.60.8

1

0 1 2 3 4 5 67Li

ch

em

ical

sh

ift

(pp

m)

[LiNO3] (M)

0

20

40

60

80

100

0 1 2 3 4 5 6

% Y

ield

Li 2

O2

[LiNO3] (M)

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.502

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

U (

V v

s Li

/Li+

)Q (mAh)

1 M LiNO3 in DMA

3 M LiNO3 in DMA

5 M LiNO3 in DMA

1 M LiNO3 DMA 3 M LiNO3 DMA 5 M LiNO3 DMA

0 0.25 0.52

2.5

3

3.5

4

4.5

U (

V v

s Li

/Li+

)

Q (mAh)

Discharge

Charge

0 0.25 0.5-10

-8

-6

-4

-2

0

Δm

O2

(um

ol)

Q (mAh)

Discharge

Charge

0.00 0.25 0.50 0.75 1.002

2.5

3

3.5

4

4.5

U (

V v

s Li

/Li+

)

Q (mAh)

Discharge

Charge

0.00 0.25 0.50 0.75 1.00-20

-15

-10

-5

0

Δm

O2

(um

ol)

Q (mAh)

Discharge

Charge

0 0.25 0.52

2.5

3

3.5

4

4.5

U (

V v

s Li

/Li+

)

Q (mAh)

Discharge

Charge

0.00 0.25 0.50-10

-8

-6

-4

-2

0

Δm

O2

(um

ol)

Q (mAh)

Discharge

Charge