R1348

Further investigation of discharging product structure in Li-O2 battery
Morgan L. Thomasa, Chihiro Yogib, Keisuke Yamanakab, Toshiaki Ohtab, Hye Ryung Byonaa

理化学研究所 Byon 国際主幹研究ユニット, b 立命館大学 SR センターaByon Initiative Research Unit, RIKEN, Wako, Saitama 351-0198 Japanb
The SR Center, Ritsumeikan University, Kusatsu, Shiga 525-8577, JapanXANES measurements were employed to characterise the discharge product for a Li-O2 battery employing
a chemically-modified carbon nanotube electrode. From those spectra, the main discharge product (lithiumfluoride) could be identified, along with side products formed during cycling, and lithium fluoride, as animportant byproduct. The role of a perfluorinated chain on the electrode was elucidated, and a potential
stability issue identified.
Keywords: Li-O2 battery, XANES, lithium peroxide, lithium fluoride, fluorinated
背景と研究目的 (Introduction)：
The reversible electrochemical reaction oflithium and oxygen hold great promise for
implementation in electric vehicles. The
non-aqueous system provides the greatest
promise in terms of theoretical energy density.1,2
Although first reported in 1996,3 thedevelopment of this battery technology has been
hindered by a number of key challenges.
In our earlier investigations, we observed thetypical discharge product (lithium peroxide)
when using a fluorinated component covalently
attached to the carbon cathode material (in thiscase, carbon nanotubes).4 Further study of thissystem is necessary to determine the role offluorine, and here we report an XAS
investigation.

結果、および、考察 (Results and Discussion)：
We undertook additional analysis to identify theprinciple chemical species present during
cycling.

実験 (Experimental)：i) Synthesis and cell fabrication
Electrodes comprised of multi-walled carbon
nanotubes (MWCNTs), with sidewalls modified
with a perfluorinated chain, were synthesized andcharacterized as previously described.4ii) Electrochemical evaluation
Galvanostatic discharge/charge was performed
using a battery cycler (WBCS3000, WonATech,
Korea). The applied current (mA.g-1) wascalculated based on the total cathode mass(including covalently bonded perfluorinatedchains).
iii) Characterisation
XANES spectra were collected at BL2 of The SR
Center, Ritsumeikan University, for Li, F, C andO K-edge.

Fig. 1. XANES spectra from modified electrodes(current density 14 mA.g-1) and standards forcomparison.
As evident in the O K-edge spectra shown in Fig

1. (top left), the principle product after the firstdischarge (1DC) is lithium peroxide. However,after the third discharge (3DC), and subsequently
the third recharge (3RC), the presence of sideproducts such as lithium acetate (CH3CO2Li) andlithium formate (HCO2Li) is noted. Theseproducts are further observed in the C K-edge
spectra (Fig 1. top right).
Moreover, the Li K-edge and F K-edge spectra
identify the presence of lithium fluoride (LiF) inthe electrodes. It is clear that this is a sideproduct formed initially during the first discharge,
and is present thereafter.
In summary, we have demonstrated the use of aperfluorinated modification on a carbon cathodein the Li-O2 battery. The stability of the C-F bondis questionable, as evident from our XANES
measurements, which has important implications
for other work being carried out with Li-O2batteries, where perfluorinated binders are often
employed.
Moreover, with the aid of the XANES analysis,
we have been able to determine the chemical
nature of the discharge products, a key findingthat will allow us to propose a mechanism for theenhanced performance when these modified
electrodes are employed.
文 献 (References)[1] J. Christensen et al., J. Electrochem. Soc.,
2012, 159, R1-R30.
[2] J. P. Zheng et al., J. Electrochem. Soc., 2008,
155, A432-A437.
[3] K. M. Abraham and Z. Jiang, J. Electrochem.
Soc., 1996, 143, 1-5.
[4] M. L. Thomas et al., The SR Center,
Ritsumeikan University, FY2013 report R1307,
R1329.
論 文 ・ 学 会 等 発 表 （ 予 定 ） (Articles andmeetings)
Articles[1]M.L. Thomas and H.R Byon, Role of fluorine
as a surface modifier in the non-aqueous
lithium-oxygen battery, in preparation.
Meetings[1] M.L. Thomas, K. Yamanaka, T. Ohta, and H.
R. Byon, “Role of Grafted PerfluorinatedMoieties on Porous Carbon Cathode for theLi-O2 Battery”, Electrochemical Conference on
Energy & the Enviroment (Shanghai, China),
13-16 March 2014. (Oral Presentation)