|dc.contributor.advisor||Bhattacharyya, Aninda Jiban||
|dc.description.abstract||In this thesis, we have attempted to understand the working principle of Li(Na)-S(Se) battery
and following such understandings we have attempted towards the design of various S(Se)-
cathode materials for the alkali based chalcogen batteries. In the final chapter, we have
focussed on the development of anode materials for full Li-ion cell. The summary of the
various chapters is as follows.
Chapter 2 discusses about NaY-xS-PAni exhibiting remarkable electrochemical performance
as a cost-effective sulfur cathode for rechargeable Li-S batteries. The superior
electrochemical stability and performance of the NaY-xS-PAni is directly correlated to the
novel NaY electrode structure in combination with the host polarity and ionic conductivity.
The zeolite provides an optimum geometrical and chemical environment for precise
confinement of the sulfur while the polyaniline coating provides electron conduction pathway
along with extra polysulfide confinements. This cathode material exhibits very stable cycling
for more than 200 cycles with relatively low specific capacity and modest rate capability. To
develop a material for obtaining high specific capacity value we moved to carbon based host
and the details are covered in chapter 3 and 4.
To summarize Chapter 3, we have successfully extended the pressure induced capillary
filling method for confinement of sulfur and selenium in the interior core of the MWCNTs.
This method results in ultra-high loading yields of the chalcogens inside the MWCNTs. The
ensuing composites S-CNT have been convincingly demonstrated as prospective cathodes in
Li-S rechargeable batteries exhibiting very high specific capacities ~ 1000 mAh g-1 at C/10
current rates. The novelity of this host has been established by extending the work in
encapsulating Se with the similar protocol and studying its electrochemical activity. The high
efficiency of the Li-S/Se electrochemical reaction observed here is directly attributed to the
efficacy of the encapsulation protocol of S/Se inside the CNTs. The
polyselenides/polysulfides are completely confined within the precincts of the CNT cavity
leading to an exceptionally stable battery performance at widely varying current densities.
With the success of this encapsulation technique for the carbon based host, we developed
another interconnected mesoporous microporous carbon host for sulfur encapsulation the
details of which constitute the next chapter.
In chapter 4, we have discussed here a novel S-cathode where the sulfur confining
hierarchical carbon host synthesized using a sacrificial template can be very effectively
employed for in Li-S rechargeable battery. The hierarchical mesoporous-microporous
architecture comprising of both mesopores and micropores provide an optimal potential
landscape which in turn traps high amounts of sulfur as well as polysulfides formed during
successive charge-discharge cycles. The uniqueness of the carbon matrix translates to
exceptionally stable reversible cycling and rate capability for Li. Such promising result with
Li-S battery compelled us to check the performance with Na anode. This led to the
development of intermediate temperature Na-S battery with JNC-S as the prospective
cathode. It is envisaged that such materials design will be very promising in general for
battery chemists especially for higher valent metal-sulfur systems (e.g. magnesium,
aluminum). The host discussed here will be ideally suitable for introduction of dopants such
as nitrogen, boron, thus enhancing it’s versatility as a heterodoped mesoporous-microporous
host for varied applications.
In all the preceding chapters, the focus was to encapsulate sulfur in some host structures.
Chapter 5 deals with an alternative configuration for the Li-S battery that uses an oxide based
interlayer to restrict the polysulfides. From the study discussed here, it can be concluded that
NiOH-np/NiO-np can act as an efficient interlayer material for superior anode protection. The
interlayer provides an anchor to hold back the polysulfides primarily on the cathode side by
forming intermediates such as NiS3(OH) and NiS4(OH). Although, the specific capacity is
less compared to the theoretically estimated value for S-cathode, the high cyclability coupled
with extremely good rate capability performance makes this a very promising configuration
of Li-S cell assembly for practical applications and deployment. The success of this strategy
is expected to decrease the need for design of sophisticated S-scaffolds and lead to simpler
Li-S rechargeable batteries.
After an extensive discussion on development of cathodes for alkali based chalcogen
batteries, we shifted gears and tried our hands in developing some eco-friendly anode
materials. The details of graphitic carbonitride as an anode material for Li-ion cell has been
discussed in chapter 6. To conclude, we have discussed here in detail the unique layered
structure of the as-synthesized gCN and its impact on the intrinsic charge transport properties.
Both factors eventually determine their electrochemical performance. The gCN discussed
here is obtained using a very simple synthesis protocol in large yields from a very cheap
organic precursor. The work highlights again the important role of chemical composition and
structure on the functionality of the intercalation host. These have a strong bearing on the
electronic charge distribution in the host and its eventual interaction with the intercalating
ions. Compared to several non-trivial layered carbonaceous structures, the gCN interestingly
displays 3-D ion transport. Additionally, it also sustains facile electron transport (2-D) despite
the low concentration of carbon. In spite of the modest specific capacities as observed in case
of the half cells, the gCN when assembled with (high) voltage cathodes in full Li-ion cells,
the performance is quite encouraging. To the best of our knowledge this is for the first time
that graphitic carbon nitrides have been demonstrated as an anode in full Li-ion cells. The
potential of majority of the reported high surface area and high capacity complex
carbonaceous structures in Li-ion cells are inconclusive. This is mainly due to the fact that the
percentage of reports on full Li-ion cell performance is very rare. The full cell analysis of the
gCN discussed here conclusively rules out the necessity of the requirement of high specific
capacity materials in practical/commercial full cells. We envisage that the work discussed
here will pave the way for synthesis of many such electrode materials from renewable
resources resulting in the development of green and sustainable batteries.
Overall we have been able to address some of the potential problems of Li-S and Li-ion
battery systems. There is further scope of betterment with extensive study and this work
opens the scope for it in future.||en_US
|dc.rights||I grant Indian Institute of Science the right to archive and to make available my thesis or dissertation in whole or in part in all forms of media, now hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part
of this thesis or dissertation||en_US
|dc.subject||Graphitic Carbon Nitrides||en_US
|dc.title||Investigations of Chalcogen-Cathodes and a Carbonitride-Anode for Alkali-Based Rechargeable Batteries||en_US
|dc.degree.grantor||Indian Institute of Science||en_US
|dc.degree.discipline||Faculty of Science||en_US