Applications Note

QuantumLeap XAS

Observing Lithium Ion
Battery Bonds During
Charge Cycling Using
Laboratory XAS
X-ray Absorption Spectroscopy (XAS) analyses of measurement results
obtained with QuantumLeap H2000 for low-Co (<3-5% wt.) Li-ion NMC
batteries are presented. High quality EXAFS were obtained for Mn and Ni
in transmission mode, while Co was obtained using fluorescence mode.
Mn-O and Co-O indicated reversible/minimal changes, while Ni-O showed
Jahn-Teller distortion that indicated different Ni oxidation states.
This applications note discusses battery science enabled by Sigray QuantumLeap XAS

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Applications Note

Observation of Jahn-Teller Distortion Effect on Ni-O bonds in Lithium Based NMC
batteries during cycling process using QuantumLeap H2000
Author: Dr. Aniruddha Deb, Dr. Srivatsan Seshadri | Sigray, Inc.

Background: A sustainable future with renewable energy
requires development of efficient energy storage systems
with high energy density that are both competitive and costeffective when compared with currently used energy sources
like natural gas, coal and oil. Lithium-ion batteries (LIBs)
have attracted the technological market due to its promiseof high energy density ~800 Wh/kg. In LIBs, the intercalationof Lithium ions (Li+) affects the atomic and the electronic
structure of the cathode material. This intercalation effectbetween the electrodes (cathode and anode) exploits diverse

Novel Approach: Sigray QuantumLeap XAS
Sigray’s QuantumLeapTM H200 is a laboratory x-ray
absorption spectroscopy (XAS) instrument that provides
synchrotron-like capabilities and features:•a patented ultrahigh brightness x-ray source,•wide energy range coverage from 4.5 to 25 keV,•cylindrically curved Johansson crystals,•a highly efficient data acquisition approach,•both transmission and fluorescence mode measurement
options allowing analyzing samples with concentrations

and complex chemistries that need to be understood at theatomic level to enable designing efficient electrode systems
with excellent electrochemical behavior, energy density, andcycling behavior that correlates with better life cycles.
X-ray absorption spectroscopy (XAS), a powerful techniquethat provides element specific short range structuraland coordination environments, allows the scientists toinvestigate the influence of repeated cycling of the electrodeon the oxidation state, the coordination environment, andstructural changes. To date, XAS is predominantly performedat synchrotron facilities because they provide tunable energy
x-ray beams of high brightness [1,2].

However, difficultaccessibility, limited beamtime, and challenging logistic
issues limit the scope of their use and preclude the possibilityof using them for routine measurements. Laboratory based
XAS instruments such as Sigray QuantumLeap can enable
academic and industrial researchers to perform routine
measurements and analyses to shorten the time scales

as low as 0.1% wt, and•customizability to enable operando experiments undervarious environments.

MethodAll data was acquired on QuantumLeap H2000 using aGe(331) crystal. Co K-edge measurements were made in thefluorescence mode due to its low concentration (~3-5 wt.%),while the Mn and Ni edges were measured in the transmission
mode. For all measurements, k-range of ~12 was chosen.
Acquisition times were deliberately kept long (details givenin the next section) to get very high Signal to Noise Ratios(SNR) for accurate analyses. However, the acquisition
times can be reduced by >3X for quick measurements for
qualitative analyses. The obtained results were processedin the QuantumLeap GUI and then imported to Athena andArtemis program suite of the IFEFFIT package [3] for furtheranalysis.

involved to develop novel high efficiency electrode systems.

2Applications NoteExperiments and Results
The Mn K-edge spectra for a fully charged and discharged
electrode were collected in 12 hours (Figure 1). The weak preedge feature at ~6543 eV is clearly visible due to high SNR inthe data.

Figure 2: Low concentration of Co ~3-5% by wt.% in NMC electrodes
charged and discharged. Only about 100eV of the scan is shown.

Figure 1: Mn-K edge of NMC electrodes fully charged and discharged.
Comparison of the MnO2 model and Mn foil oxidation states shows that
Mn in NMC are in an oxidation state of ~4+. The absorption edge energy
does not change much showing that Mn acts as a spectator during
cycling.

The weak pre-edge feature observed for both charged
and discharged states is indicative of the retention of theFigure 3: EXAFS of low concentration of Co ~3-5% by wt.% in NMC
electrodes charged (blue) and discharged (red).

octahedral coordination environment (MnO6) as opposed tothe tetrahedral environment which would result in a strong

The Fourier transform magnitude (FT) for Mn and Co in

pre-edge intensity. The Mn-edge between the charged and theNMC are shown in Figures 4 and 5, respectively.

discharged electrode did now show any significant rigid shift
in energy. This signifies that Mn almost acts as a spectator oris electrochemically inactive during the cycling process while
the small changes that we see in the shape of the Mn-spectra
show the possible change in the local structure around the Mnatom. The XANES shows good agreement between observed
Mn-edge energy and the model compound (MnO2) suggestingthat the Mn is in a state of Mn4+ during cycling.
Figures 2 and 3 show the XAS data across the Co K-edge
measured in the fluorescence mode. The concentration of Co
is around 3-5% by weight and about 18 hours of acquisition
was required to obtain high SNR EXAFS data up to k=11.

Figure 4: Mn K-edge FT-EXAFS of NMC along with model systems
showing the main peak at ~1.5 Å (uncorrected phase) corresponding
to Mn-O bond and the second peak at ~2.3 Å corresponding to Mn-Mbond3

Applications Note

This bond-length change beween charged and discharged
states is consistent with the fact that when charged, thenickel goes to the form of ~Ni4+ which is non-Jahn–Teller anddoes not suffer from Jahn–Teller distortion, and this results
in a shorter bond distance of ~Ni4+-O bond (~1.3 Å). On thecontrary, in the discharged sample, there might be somepresence of Ni in Ni3+ or a mixture of Ni3+/Ni2+ state. Since
Ni3+ is Jahn–Teller active, the discharged sample shows alonger Ni3+-O bond distance of ~1.7 Å. The shorter Ni-O bonddistance seen in Figure 6 for the charged sample can also beFigure 5: FT-EXAFS of Figure 3, showing the comparison of the charged
and discharged state of the NMC electrodes.

explained from the oxidation state picture since Ni4+ in thecharged sample has a shorter ionic-radii (0.46 Å) compared tothe discharged sample with Ni2+/Ni3+ with a larger ionic-radii

In both figures 4 and 5, the first peak ~1.4 Å is attributed to the(0.69 Å/0.56 Å).

Mn-O/Co-O interactions, while the second peak ~2.3 Å (nonphase shifted) is due to the M–M (metal-metal) interactions.

We can also see that the Fourier Transform (FT) amplitude ofFor both Mn and Co, the first peak did not show any drastic

the first shell remains the same (Figure 6) for both charged

shift between charge and discharge state, which indicatesand discharged samples, signifying that the local Ni-O

reversible/minimal changes in the Mn-O/Co-O distances on

coordination environment is preserved during cycling. Butcycling. But as seen on Figure 6, the first peak attributed to thethe FT amplitude of the second peak (~2.3 Å) is not the same

Ni-O shows a change with the Ni-O bond distance increasingfor charged and discharged states, indicating that the Ni-Ni

in the discharged sample (1.3 Å to 1.7 Å, non-phase shifted).

coordination environment may have changed during cycling.

1 mm

SummaryStudies of the current set of Li-ion NMC battery samples using
Sigray QuantumLeap was performed using both fluorescence(for Co) and transmission mode XAS (for Ni and Mn). Results
show that Mn is electrochemically inactive and in octahedral
coordination. The bond lengths of Mn-O and Co-O are shown
to change minimally in the charge-discharge cycles. The Ni-O
bond length changes due to Jahn-Teller distortion, indicating
different

Nispecies

betweenthecharged/discharged

samples. Local environment changes are not seen for Ni-O,
but they are seen in for Ni-Ni. The above results demonstrate
Figure 6: FT-EXAFS of Ni in NMC, showing the comparison of the charged
and discharged state of the NMC electrodes along with the model systems.

the synchrotron-like capabilities of a laboratory XAS tool to
produce the quality of data required for detailed and accurate
analyses to understand NMC electrode’s behavior undercycling conditions.

REV20231017
1. WS Yoon, CP Grey, M Balasubramanian, XQ Yang and J McBreen, Chemistry of Materials 15 (2003) p. 3161-3169.
2. J Timoshenko, D Lu, Y Lin, and AI Frenkel, The Journal of Physical Chemistry Letters 8 (2017) p. 5091-5098.
3. B Ravel and M Newville, ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT, Journal of Synchrotron Radiation 12, 537–541 (2005).

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P: +1-925-446-4183
www.sigray.com
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