Novel Electrolytes for use in Li-Air Batteries for NASA Electric AircraftRocco P. Viggiano*, Donald Dornbusch*, William Bennett*, Kristian Knudsen§, Baochau Nguyen†
*NASA Glenn Research Center, 21000 Brookpark Rd, Cleveland, OH 44135; §UC Berkeley, Berkeley, CA 94720;†Ohio Aerospace Institute, 22800 Cedar Point Rd, Cleveland, Ohio 44142
IntroductionThe 2018 Strategic Implementation Plan sets forth theNASA Aeronautics Research Mission Directorate(ARMD) vision for aeronautical research aimed at thenext 25 years and beyond. It encompasses a broad rangeof technologies to meet future needs of the aviationcommunity. Two key areas of focus are the transition toultra-efficient subsonic transports as well as the transitionto safe, quiet and affordable vertical lift air vehicles. Insupport of these technology areas, NASA has beenresearching hybrid-electric as well as fully electricaircraft designs.
Both designs necessitate the development of higherenergy density battery systems. Lithium-oxygen batterieshave been proposed as a potential enabling technologyowing to its high theoretical energy density, to date thehighest of any proposed battery technology.
However, there are immense technical challenges facingtheir development, including the development of morestable cathodes and electrolytes. Through a synergisticapproach utilizing computational modeling andexperimental screening, several new cathode andelectrolyte candidates have been screened. Concurrently,decomposition analysis of candidate electrolyte systemsusing nuclear magnetic resonance (NMR) spectroscopyhas yielded mechanistic insight into decompositionpathway, which is vital to the development of futurestable electrolyte candidates.
ConclusionsLinear Amides (NMA, DMA) Interestingly more 12Cx,xO is formed during charge relative to
other solvents, suggesting more simple products are formed
Low amounts of 12C18,18O2 is formed, suggesting solvent is relatively stable towards Li2O2 and its intermediates
DMA shows the best stability of the amides/ureas tested, but decomposes through a Baeyer-Villiger oxidation method
Linear Urea (TMU) Relatively low amounts of 12C18,18O2 formed, is more stable
towards Li218,18O2/Li18,18O2/18,18O2
- than linear amides
Cyclic Ureas (DMI and DMPU) Large amounts of 12C16,18O2 and 12C18,18O2 are formed while
low amounts of 12C16,16O2 is formed
This suggests an increased activation of a different pathway where CO2 is formed from Li2O2 induced solvent reduction
Results
Results
ExperimentalDifferential electrochemical mass spectrometry (DEMS) and nuclear magnetic resonance (NMR)spectroscopy were performed on a series of amides and ureas to elucidate the decompositionmechanism of these two classes of electrolytes. Figure 2 shows the series of amides and ureastested.
Figure 4: NMR spectra of neat DMA and the products formed after 1 cycle
Figure 3: NMR spectra of neat NMA and the products formed after 1 cycle
Scheme 1: Baeyer-Villiger Oxidation of acetamide electrolytes
Figure 5: DEMS analysis performed for NMA and DMA in 1M LiNO3
State-of-the-art Electrolyte
Figure 2: Series of acetamide, linear urea and cyclic urea electrolyte candidates
1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidione
(DMPU)
N,N-Dimethylacetamide(DMA)
N-Methylacetamide(NMA) Tetramethylurea
(TMU)
1,3-dimethyl-2-imidazolidinone
(DMI)
1,2-dimethoxyethane(DME)
LFP
NMADMA
• Decomposition occurs predominantly on discharge
• No difference is observed between a Li anode or LFP anode
• YLi2O2,c /YLi2O2,d = ∼0.91-0.99
• Solvent degradation occurs on discharge, suggesting reductive mechanism
• 1H NMR needed to understand mechanisms
DMSO
AB
BA
C
Assignment Shift (ppm)A 1.98B 2.80C 7.5
H3C NH
O
CH3
DMSO
ABBA
CAssignment Shift (ppm)
A 1.98B 2.80C 7.5
H3C NH
O
CH3
C
C O
H
H
H H
Assignment Shift (ppm)E
F
3.484.80
E F
EF
Assignment Shift (ppm)G 2.09
G
G Assignment Shift (ppm)J 2.91K 6.98
J
K
J
K
H2O HDO
H2ODMSO
HDO
H3C N
O
CH3
CH3
BA
C
ABC
Assignment Shift (ppm)A 2.077B 2.78C 2.94 H2O
DMSO
HDO
H3C N
O
CH3
CH3
BA
CABC
Assignment Shift (ppm)A 2.077B 2.78C 2.94
C O
H
H
H H
Assignment Shift (ppm)E
F
3.484.80
E
EF
FAssignment Shift (ppm)
G 2.09
G
G
OER/ORR = 0.74
OER/ORR = 0.79
OER/ORR = 0.77OER/ORR = 0.34
OER/ORR = 0.14
Figure 6: CO2 evolution overview of selected amide and urea electrolytes with a focus on solvent 12C
Figure 1: OER/ORR ratio of selected electrolytes and DEMS analysis of state-of-the-art electrolyte DME
