Polymer-Oxide Anode Materials
- PDF / 379,154 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 100 Downloads / 222 Views
and
[PANI] 0 .34HMWO 6
(M=Ta,Nb) have each shown that this
incorporation demonstrates enhanced ion and/or electronic transport on galvanostatic cycling over that of the pristine transition metal oxide.1' 23 In addition, the redox capacity of the intercalated PANI provides a moderate increase in cell capacity, and improves the reversibility of the Li insertion reaction. In the case of [PANI]o.44 V20 5 and [PANI]o. 34HMW0 6 the Li chemical diffusion coefficients were found to be greater for the nanocomposites compared to the transition metal oxides by over one order of magnitude. The improved kinetics appear to be the result of a lower energy pathway for Li ion migration in the nanocomposites. This may due to the polymer propping the oxide layers apart, thus modifying the Li insertion sites, and shielding the lithium ions from the polarizing effect of the oxide. The effect is most pronounced at small amounts of Li intercalation, but suppressed as more lithium is inserted. Molybdenum trioxide has been primarily considered as a 2V material in Li batteries due to topotactic Li insertion at that potential. A recent study by Leroux and Nazar 4, however, shows that sodium molybdenum bronze ([Nao. 26 MoO 3 ]) demonstrates good electrochemical performance at low potential in the range 3-0.005 V vs. Li, albeit with substantial cell polarization leading to an average charge potential of 1.3V. With this in mind, and the fact that no known investigations of polymer-oxide nanocomposites as negative electrodes have been reported, a study of the low potential electrochemical performance of the material formed from the incorporation of an electronically conducting polymer between the layers of MoO 3 was instituted. Most polymers are not stable to cycling at low potential. Nevertheless, recent studies by Dubois and Billaud have reported that poly(para-phenylene) can reversibly intercalate 0.5Li between 500-OmV with low polarization (after initial irreversibility has subsided).5 PPP is known to be a fairly crystalline polymer that is infusible and insoluble. This presents a challenge to develop a synthetic method to incorporate the 499 Mat. Res. Soc. Symp. Proc. Vol. 496 ©1998 Materials Research Society
polymer chains within the van der Waals region. Herein we report the synthesis of the novel polymer-oxide composite, PPPNH 2-MoO 3, its characterization, and initial electrochemical and cycling behavior studies.
EXPERIMENTAL Synthesis and characterization. The molybdenum bronze [Lio.o7Nao0. 3(H 20)o. 40]MoO 30.20°, was prepared as described previously, by the reduction of MoO 3 in a Li 2MoO 4 buffered aqueous solution.6 The lithium bronze [Li"x(H 20)JMoO3 (LiMoO 3 ) was prepared7 by reduction of MoO 3 with LiBH 4 in diethyl ether, as reported by Kanatzidis and Marks. Poly(para-phenylene) was prepared by the Kovacic method of oxidative polymerization of benzene using AIC13 with a CuC12 catalyst.8 The amino derivative form of the polymer was prepared by first nitrating the phenylene in mixed HNO 3/H 2SO4 acid, followed by reduction
Data Loading...
