Journal of The Electrochemical Society, 155 ͑10͒ A775-A782 ͑2008͒
A781
more stable during cycling. Although only results of first cycle have
been obtained, it can be expected that the electrolyte will be more
endurable for extended cycling after AlF3 coating, which is one of
the crucial reasons accounting for the improved electrochemical per-
formance of the coated materials. In addition, it has also been found
that the amount of gaseous product of CO2 decreased significantly
in the following cycles. The detailed work and further research on
the electrolyte decomposition mechanism is still ongoing in our lab.
Conclusion
The Li͓Li0.2Mn0.54Ni0.13Co0.13͔O2 samples coated with AlF3
have been prepared and investigated. The AlF3-coated
Li͓Li0.2Mn0.54Ni0.13Co0.13͔O2 exhibited superior electrochemical
performance in comparison with the pristine material, including
high initial discharge capacity of 267 mA h/g, low initial irrevers-
ible capacity loss, better cyclic performance, and higher rate capa-
bility. Meanwhile, the thermal stability of the materials was also
improved significantly after AlF3 coating. The improved electro-
chemical performance could be attributed to the “buffer” layer pro-
vided by AlF3 coating, through which oxygen atoms with high ac-
tivity generated at high potential combined to form O2 molecules
with low activity. Consequently, it results in the reduction of the
activity of the evolved oxygen species and suppression of the de-
composition of electrolyte. This effect has resulted in less oxidation
of electrolyte components, prevented the electrode/electrolyte inter-
facial degradation, and thus suppressed the increase of charge trans-
fer resistance.
Acknowledgments
This work was financially supported by the National Basic Re-
search Program of China ͑973 Program͒ ͑grant no. 2007CB209702͒,
and National Natural Science Foundation of China ͑NNSFC, grant
no. 20433060, grant no. 20473068, and grant no. 29925310͒.
Figure 12. ͑Color online͒ DEMS measurements of the CO2 evolution on
Li͓Li0.2Mn0.54Ni0.13Co0.13͔O2 electrodes. ͑a͒ Pristine and ͑b͒ AlF3-coated
sample.
Xiamen University assisted in meeting the publication costs of this ar-
ticle.
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