488
doi:10.1017/S1431927614004164
Microsc. Microanal. 20 (Suppl 3), 2014
© Microscopy Society of America 2014
Quantitative Oxidation State Analysis of Transition Metals in a Lithium-ion Battery
with High Energy Resolution AES
A. Tanaka, K. Tsutsumi , H. Onodera and T. Tazawa
JEOL ltd., Musashino 3-1-2, Akishima, Tokyo, Japan
After a first suggestion of the use of lithium transition-metal oxides in the cathode of lithium-ion battery
(LIB) [1], many researchers have investigated to improve its performance such as higher-energy density,
longer-life, and lower-cost. For the systematic, effective development, various transition-metals for the
cathode active material have been investigated and chemical state characterization have earnestly been
desired of small particles with a size of less than one micrometer.
Auger electron spectroscopy (AES), which is well-known as a powerful method to detect lithium like Xray photoelectron spectroscopy (XPS), is best suited for the above purpose. Auger spectra have been
known to have chemical state information as a peak shift and a peak shape change [2], and the chemical
state analysis based on standard spectra measured with high energy resolution of ΔE/E=0.1% is an
effective method for complex shape Auger spectra [3].
In this study, we focused on the manganese oxides which have been one of the attracted materials as a
low-cost cathode active material for a LIB. The previous attempt to identify oxidation state of
manganese with AES did not lead to a fruitful result [4]. The reason is that chemical state analysis was
mainly based on the shift of the peak positions of the Mn MVV spectra. Unfortunately no appreciable
change in the peak positions was observed due to oxidation states of manganese. Beside, the Mn MVV
spectrum is situated in the low energy region between 30 and 100 eV where the spectra of many other
elements appear, which fact may cause difficulty in the separation of manganese components from
superimposed spectra. In the application to the LIB, especially, the Mn MVV spectrum inevitably
overlaps with the lithium spectrum because the peak positions of Mn MVV and Li KVV are located at
around 50 eV. In this presentation, the Mn LMM spectra of three oxidation states: Mn0(metal),
Mn2+(MnO), and Mn4+(MnO2) were measured for standard spectra, using high purity metal and oxides,
with a higher energy resolution of 0.1% with a commercial Auger electron spectrometer equipped with a
field emission gun and a hemi-spherical analyzer with variable energy resolution (0.05-0.5%): JAMP9510F (JEOL Ltd.). These were added to our file of standard spectra, consisting of a large number of
spectra of elements with well defined chemical states. No noticeable differences were detected in their
peak positions, but appreciable differences were observed in their shapes. The latter differences were
large enough for superimposed spectra to be separated into each individual oxidation state spectrum as
shown in Fig.1.
Moreover, we applied the chemical state analysis with the standard spectra to the depth profile of
composition result for two different types of particle used as a cathode active material: one contains an
appreciable amount of lithium, the other contains less lithium, with an energy resolution of 0.1%. Fig.2
shows that the oxidation state of manganese in the particle containing lithium was mainly Mn4+, whereas
that of manganese in the particle containing less lithium was mainly Mn2+. The oxidation state
difference due to the amount of lithium was observed for each particle.
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Microsc. Microanal. 20 (Suppl 3), 2014
489
The present study confirms the very high potential of our recently developed method of oxidation state
analysis with higher energy resolution AES. Moreover we will discuss the possibility of quantitative
analysis of chemical state of manganese by the use of the absolute intensity of standard spectrum[3].
References:
[1] J.B. Goodenough et al., US patent, 4302518(1981)
[2] Madden, H. H., Journal of Vacuum Science and Technology, Vol.18 (1981), p.677
[3] K.Tsutsumi et al., Journal of the Surface Science Society of Japan Vol.33 (2012), p.431
[4]S. Singh et al., Appl. Surf. Sci. 152 (1999), p. 213
Intensity [dN(E)/dE]
Mn0
Mn2+(MnO)
Mn4+(Mn2O)
520
540
560
580
600
620
640
Electron energy (eV)
Figure 1. Mn LMM spectra of Mn0 (metal), Mn2+ (MnO) and Mn4+ (Mn2O)
70
70
Probecondition(10keV, 10nA)
Probecondition(10 keV, 10 nA)
60
60
Ar sput.( 300eV, 15s/cycle)
rate: 1.2nm/min asSiO2
Ar sput.( 300eV, 15s/cycle)
rate: 1.2nm/min asSiO2
50
50
Atomic %
Atomic %
2-
O2-(MnO2)
40
2+
Mn (MnO)
30
O2-(MnO)
O (MnO2)
40
30
Mn4+(MnO2)
20
20
Li
Li
O(-Li)
2+
Mn (MnO)
O2-(MnO)
10
10
4+
Mn (MnO2)
O(-Li)
0
0
0
5
10
15
20
25
Etchingtime(min)
30
35
0
5
10
15
20
25
30
35
Etchingtime(min)
Figure 2. The depth profile of the atomic concentration of each chemical state for two different types
of particle used as a cathode active material
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