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Application News
No. P113
Electron Probe Microanalyzer EPMA-8050G
Analysis of Positive Electrode of Lithium Ion Battery
Introduction
Lithium ion batteries (LIB) are storage batteries in which the cell is charged and discharged by desorption/insertion of lithium ions (Li+) in the structure of the active material. The applications of LIB have expanded dramatically in recent years, and active research is underway with the aims of achieving higher capacity, longer life, lower cost, and improved safety. The main components of a LIB are the positive electrode, negative electrode, separator, and electrolytic solution, and among these, the positive electrode is the key element for enhanced performance. The positive electrode has a structure in which a mixture of the active material, binder, and conductive additive are coated on a collector made of aluminum foil. Evaluation of the distribution of these components is important in improvement of cell performance, quality control, and failure analysis. This article introduces an example of analysis of the positive electrode of a LIB using a Shimadzu EPMA-8050G EPMA™ electron probe microanalyzer.
T. Ono
Positive Electrode Materials In positive electrodes, a material which is capable of maintaining a stable structure during desorption/insertion of Li+ is used as the active material. The mainstream active materials in the market are lithium nickel cobalt manganese oxide (Li(Ni-Co-Mn)O2), lithium nickel cobalt aluminum oxide (Li(Ni-Co-Al)O2), spinel-type lithium manganate (LiMn2O4), and olivine-type lithium iron phosphate (LiFePO4)(1).
Analysis of Positive Electrode Surface The object of this analysis is a positive electrode of a lithium ion battery cell which was prepared using the materials shown in Table 1, and was disassembled in the 100 % charged condition. The active material of the positive electrode is spinel-type lithium manganate (LiMn2O4). Because this electrode is inexpensive, offers highsafety, and is suitable for large capacity discharge, it is widely used in rechargeable batteries (secondary batteries) of hybrid electric vehicles. Fig. 1 is the result of a mapping analysis of the surface of this positive electrode and shows the distribution of the main elements. O and Mn show the distribution of the active material, F shows the binder and supporting electrolyte (LiPF6), C shows the binder and conductive additive, and P shows the supporting electrolyte.
Table 1 Materials of Lithium Ion Battery
Class Material
Positive electrode
Active material LiMn2O4
Collector Al
Binder PVDF
Conductive additive Acetylene black
Separator 3-layer microporous membrane
Glass filter
Electrolytic solution
Supporting electrolyte LiPF6
Solvent EC/DEC
Additive VC
(Sample provided by the National Institute of Advanced Industrial Science and Technology (AIST).)
Fig. 1 Mapping Analysis of Positive Electrode Surface
10 μmSE 15.0 kV 60×45 μm 10 μmCOMPO 15.0 kV 60×45 μm 10 μmC Ka 15.0 kV 60×45 μm
(counts)nts)1230
30
1080
930
780
630
480
330
180
10 μmO Ka 15.0 kV 60×45 μm
(counts)nts)5640
200
4960
4280
3600
2920
2240
1560
880
10 μmP Ka 15.0 kV 60×45 μm
(counts)74
10
66
58
50
42
34
26
18
10 μmMn Ka 15.0 kV 60×45 μm
(counts)6000
200
5275
4550
3825
3100
2375
1650
925
10 μmOverlay
C8.1 %
24.6 %
4.9 %
56.8 %
10 μmF Ka 15.0 kV 60×45 μm
58(counts)
10
52
46
40
34
28
22
16
F+P
C+F
O+Mn
First Edition: Oct. 2020
For Research Use Only. Not for use in diagnostic procedure.
This publication may contain references to products that are not available in your country. Please contact us to check the availability of these products in your country. The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. Shimadzu disclaims any proprietary interest in trademarks and trade names used in this publication other than its own. See http://www.shimadzu.com/about/trademarks/index.html for details. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice.
© Shimadzu Corporation, 2020
www.shimadzu.com/an/
ApplicationNews
No. P113
Analysis of Positive Electrode Cross Section Next, a cross-sectional sample of the positive electrode was prepared and analyzed. Fig. 2 is the result of a mapping analysis of the positive electrode cross section. In all the element distribution images, the upper side is the aluminum foil of the collector and the lower side has a composition consisting mainly of the active material. Comparing the distributions of each element, the distributions of C and F, O and Mn, and F and P are generally in agreement. Therefore, the area ratios of the respective elements can be represented by the overlay at the lower right in Fig. 2, in which areas where C and F overlap (binder) are shown in yellow, areas where O and Mn overlap (active material) are shown in red, areas where F and P overlap (supporting electrolyte) are shown in blue, and other C-rich areas (conductive additive) are shown in green. Although both the binder and the electrolytic solution contain F, if F is identified from the combination of its distribution with C or P, it can be understood that F is concentrated in the collector side as part of the electrolytic solution. Similarly, C is present in both the binder and the conductive additive, but
can be identified from the combination of its distribution with F. Fig. 3 shows the result of a mapping analysis in which the area enclosed by the yellowish-green square in the COMPO image in Fig. 2 (top row, center) was magnified 10,000 times. Not only coarse particles with sizes of several μm, but also fine particles with sizes of less than 1 μm, the condition of boundaries and the element distribution can be observed.
Conclusion A mapping analysis of the surface and cross section of a positive electrode of a lithium ion battery, in which spinel-type lithium manganate (LiMn2O4) was used as the active material, was carried out by EPMA. The distributions of the active material, binder, conductive additive, and electrolytic solution could be understood, and it was also possible to evaluate the fine particles and boundaries under high magnification. Thus, EPMA is an effective tool for research and development of the various materials of LIB, quality control in the manufacturing process, and failure analysis.
Fig. 2 Mapping Analysis of Full Positive Electrode Cross Section
Fig. 3 Enlarged Mapping Analysis of Active Material on Surface Side of Positive Electrode Cross Section
<Reference> Noboru Oyama, Takuhiro Miyuki, Performance Evaluation of Lithium Ion Secondary Batteries (2019)
EPMA is a trademark of Shimadzu Corporation in Japan and/or other countries.
COMPO 15.0 kV 240×180 μm COMPO 15.0 kV 80×60 μm C Ka 15.0 kV 80×60 μm
(counts)unts)1230
30
1080
930
780
630
480
330
180
F Ka 15.0 kV 80×60 μm
(counts)unts58
10
52
46
40
34
28
22
16
Al Ka 15.0 kV 80×60 μm
(counts)unts)2300
300
2050
1800
1550
1300
1050
800
550
O Ka 15.0 kV 80×60 μm
(counts)nts)5640
200
4960
4280
3600
2920
2240
1560
880
P Ka 15.0 kV 80×60 μm
(counts)unts74
10
66
58
50
42
34
26
18
Mn Ka 15.0 kV 80×60 μm
(counts)unts)5080
200
4470
3860
3250
2640
2030
1420
810
50 μm 20 μm 20 μm
20 μm20 μm20 μm
20 μm 20 μm 20 μmOverlay
C6.1 %
23.7 %
10.3 %
35.6 %
F+P
C+F
O+Mn
2 μmCOMPO 15.0 kV ×10000 2 μmO Ka 15.0 kV ×10000
(counts)nts)2500
100
2200
1900
1600
1300
1000
700
400
2 μmP Ka 15.0 kV ×10000
(counts)nts30
6
27
24
21
18
15
12
9
2 μmMn Ka 15.0 kV ×10000
(counts)nts)2300
160
2033
1765
1498
1230
963
695
428