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Abstract:
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The work presented in the thesis is centered around two important
types of cathode materials, the spinel structured LixMn204 (x
=0.8to1.2) and the phospho -oIivine structured LiMP04 (M=Fe and
Ni). The spinel system LixMn204, especially LiMn204 corresponding to
x= 1 has been extensively investigated to understand its structural
electrical and electrochemical properties and to analyse its suitability as
a cathode material in rechargeable lithium batteries. However there is
no reported work on the thermal and optical properties of this important
cathode material. Thermal diffusivity is an important parameter as far
as the operation of a rechargeable battery is concerned. In LixMn204,
the electronic structure and phenomenon of Jahn-Teller distortion
have already been established theoretically and experimentally. Part of
the present work is an attempt to use the non-destructive technique
(NDT) of photoacoustic spectroscopy to investigate the nature of the
various electronic transitions and to unravel the mechanisms leading to
the phenomenon of J.T distortion in LixMn204.The phospho-olivines LiMP04 (M=Fe, Ni, Mn, Co etc) are the
newly identified, prospective cathode materials offering extremely high
stability, quite high theoretical specific capacity, very good cycIability
and long life. Inspite of all these advantages, most of the phospho -
olivines especially LiFeP04 and LiNiP04 show poor electronic
conductivity compared to LixMn204, leading to low rate capacity and
energy density. In the present work attempts have been made to
improve the electronic conductivity of LiFeP04 and LiNiP04 by adding
different weight percentage MWNT .It is expected that the addition of
MWNT will enhance the electronic conductivity of LiFeP04 and
LiNiP04 with out causing any significant structural distortions, which
is important in the working of the lithium ion battery. |