CHAPTER 5
Summary and Scope for future work
165
Summary:
Chapter II: Synthesis and characterization of layered LiCo1/3Ni1/3Mn1/3O2
cathode with improved lithium intercalation behaviour
In an attempt to obtain single phase LiCo1/3Mn1/3Ni1/3O2 compound and to realize the
maximum capacity from the same, the sol-gel synthesis procedure has been optimized
by tuning various parameters, as mentioned below
Concentration of precursor components (Li:M ratio): Different lithium and
transition metal ratios were used (Li:M =1:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1 and
1.25;1) with a view to eliminate the co-existence of trace amount of NiO impurities
found with the LiCo1/3Mn1/3Ni1/3O2 compound prepared with 1:1 ratio of Li:M. From
XRD and Charge-discharge studies, it is understood that NiO impurity phase could be
removed successfully using Li:M=1.10:1 or 1.15:1. Of the two, electrochemical
behavior is superior for LiCo1/3Mn1/3Ni1/3O2 prepared with a Li:M ratio of 1.15:1
(167 mAh/g).
Gel formation time: A combination of citric acid as complexing agent and
ammonium per sulphate as gelling catalyst results in the rapid formation of
transparent
gel,
which
upon
furnace
calcination
yields
single
phase
LiCo1/3Ni1/3Mn1/3O2 powder. Cyclic voltametry and impedance spectral studies
demonstrate the excellent reversibility and structural stability of LiCo1/3Ni1/3Mn1/3O2
cathode. Upon cycling, LiCo1/3Ni1/3Mn1/3O2 cathode delivered a capacity as high as
162 mAh/g with a capacity retention of 99%.
Novel gelling agents: The feasibility of deploying four compounds viz., agar-agar,
carboxy methyl cellulose (CMC), corn powder and gelatin as gelling agent(sol-gel
method) and/or combustible fuel (combustion method) individually to prepare
LiCo1/3Mn1/3Ni1/3O2 compound has been explored. Charge-discharge studies were
166
carried out using LiCo1/3Mn1/3Ni1/3O2 cathodes obtained from sol-gel and combustion
methods aided by the chosen additives individually. Based on the results, it is
understood that corn starch acts as a better gelling agent (with acetate metal
precursors) and as combustible fuel (with the nitrate precursors) to produce
LiCo1/3Ni1/3Mn1/3O2 compound, capable of exhibiting a capacity of 176 mAh/g.
Time/mode of furnace heating: A rapid and lesser energy requiring hybrid
microwave assisted sol-gel method has been demonstrated to prepare layered
LiCo1/3Ni1/3Mn1/3O2 compound. An initial charge/discharge capacity of 183/176
mAh/g has been exhibited by thus prepared LiCo1/3Ni1/3Mn1/3O2 cathode.
Chapter III: Investigation on the synthesis and characterization of olivine
structured LiMPO4/C composite cathodes (M=Fe & Co) for facile lithium
intercalation behavior
Identification and adoption of a suitable synthesis methodology with optimized
synthesis parameters/conditions and the type of carbon or carbon source to improve
the electronic conductivity of LiFePO4 have been attempted to modify the physical
and electrochemical properties. Drawbacks of conventional solid state fusion method,
role of surface modifiers, solution assisted synthesis approaches involving a newer
synthesis protocol to segregate Li3PO4 impurity, adoption of optimum temperature to
prepare LiFePO4/C using solution assisted synthesis method are discussed in this
chapter. As a sequel to LiFePO4 cathode, preparation of electrochemically better
performing LiCoPO4 has been attempted to arrive at the recommendation of suitable
synthesis sequence to obtain maximum capacity from LiCoPO4/C cathode within the
safer electrochemical potential window (5.1 V).
Synthesis of LiFePO4/C using Modified Solid State Fusion (MSSF) method:
Subsequent to the understanding that solid state fusion method could not be used to
167
prepare LiFePO4/C with better lithium intercalation behavior (despite the attempts
made to modify the surface with C/Cu/CuO), a simple and carbonate anion directed
modified solid state fusion (MSSF) method has been identified to produce
morphology controlled nano rods of LiFePO4/C composite with 200 nm size. MSSF
synthesized LiFePO4/C cathodes containing 2wt.% conducting and nickel coated
graphite were found to exhibit nominal specific capacity values such as 129 and 100
mAh/g respectively. On the other hand, MSSF synthesized LiFePO4/C composite
cathode consisting of 2wt.% super P carbon has delivered 160 mAh/g capacity.
Single Phase LiFePO4/C formation and Li3PO4 Phase segregation: When
LiFePO4/C composite was synthesized at 700 °C using gelatin assisted sol-gel method,
the co-existing Li3PO4 impure phase was successfully segregated by heating the
composite in a hydrothermal set up at 200 oC for 8 h. Such a treatment has resulted in
the formation of single phase LiFePO4/C composite with a capacity of 153 mAh/g.
Single Phase LiFePO4/C and Optimization of synthesis temperature: Upon revisit,
it has been found that a temperature of 600 oC is sufficient to prepare single phase
LiFePO4/C using gelatin assisted sol-gel method that has delivered a capacity of 162
mAh/g, which is close to the theoretical capacity of LiFePO4.
Carbonate anion directed growth controlled LiCoPO4/C nanorods with
improved electrochemical behavior: Nanocrystalline LiCoPO4/C has been prepared
by adopting modified solid state fusion method, wherein H2CO3 or a mixture of
H2CO3+(NH4)2CO3 has been used as a growth inhibiting modifier to control the
growth of the particles and morphology of the final product. Formation and coexistence of Co2P phase, desirable to improve the conductivity and electrochemical
properties of LiCoPO4 has been aided by the addition of H2CO3+(NH4)2CO3 mix,
especially when heated under Ar atmosphere. An externally added 10 wt.% super P
168
carbon offers an adherent carbon coating on pristine LiCoPO4 and the resultant
LiCoPO4/C composite cathode within a potential window of 3~5.1 V has exhibited a
capacity of 123 mAhg-1 with 89 % capacity retention.
Chapter IV: Preliminary studies on electrolytes for Li-S system
The incorporation of additives for electrolyte, modification of lithium metal surface
and chemically synthesized polysulphide species as active material rather than sulphur
impregnated composites in order to eliminate the formation of Li2S within a porous
structure are the glimpse of certain explorative attempts made in the present study.
Among the different additives, small amount of toluene addition in TMS electrolyte
has improved the capacity retention (about 100 mAh/g for 50 cycles) compared with
the electrolyte without toluene. Similarly, formation of Li-Al type of films on lithium
electrode improves cycle life, but indicates the need to understand the surface
chemistry in detail using in-situ techniques, especially after few hundreds of cycles.
Two different approaches enlisting the use of either polysulphide as active
material or S deposited on Li, both aiming to eliminate detrimental formation of Li2S
at the porous carbon matrix have been made. S deposited on Li anode (SLi) and cycled
vs. kenjen black carbon cathode, leads to a new cell configuration up on progressive
cycling. Herein, lithium-polysulphide species are produced chemically and the
capacity also improves upon extended cycling. Such a simple approach exhibits
excellent electrochemical performance and promises for further understanding.
Scope for future work:
a)
Based
on
the
satisfactory electrochemical
behavior
realised
with
LiCo1/3Ni1/3Mn1/3O2 cathode, full cell assembly with select anodes and
fabrication of pouch cell with the currently synthesized LiCo1/3Ni1/3Mn1/3O2
169
cathode to validate its compatibility and suitability for large scale
applications could be investigated.
b)
Gelatin assisted sol-gel method (at 600 °C) may be upgraded for bulk
synthesis of LiFePO4/C and its suitability for high power applications may
also be examined.
c)
High voltage characteristics ( 4.7 V) of LiCoPO4/C cathode upon extended
cycling may be studied, which eventually would lead to the identification of
newer electrolyte combinations of non-aqeous electrolytes with suitable
lithium salts and/or Ionic liquids, bestowed with an extended structural
stability well behind 5.3 V limit, required for practical applications.
d)
Identification of suitable electrolyte (may be a common one for Li-ion and
Li-S system) may pave way to understood, sort out and solve issues pertinent
to the currently available Li-S system. Alternatively, protection of lithium
surface from dissolved lithium polysulfides using a liquid/solid/polymer
array may also improve the performance characteristics of Li-S system. The
following two compartment cell, upon existence may lead to separator free
Li-S battery which is an innovative approach.
170
List of Publications on Thesis based
1. On the synergetic effect of carbonate anion directed shape controlled morphology
and super P carbon in preparing LiFePO4/C cathode with improved lithium
intercalation behavior, Gangulibabu, N. Kalaiselvi, D. Bhuvaneswari, C. H. Doh,
Int. J. Electrochem. Sci., 5 (2010) 1597
2. Modified sol-gel synthesis to prepare nanocrystalline LiCo1/3Ni1/3Mn1/3O2 cathode
suitable for rechargeable lithium batteries, Gangulibabu, D. Bhuvaneswari, N.
Kalaiselvi, Nanoscience and Nanotechnology Letters, 3 (5) (2011) 717
3. Comparison of corn starch assisted sol-gel and combustion methods to prepare
LiMnxCoyNizO2 compounds, Gangulibabu, D. Bhuvaneswari, N. Kalaiselvi, J.
Solid State Electrochemistry (Article in Press) DOI: 10.1007/s10008-012-1851
4. Carbonate anion controlled growth of LiCoPO4/C nanorods and its improved
electrochemical behavior, Gangulibabu, Kalaiselvi Nallathamby, Danielle
Meyrick and Manickam Minakshi, Electrochim. Acta
(Article in Press)
DOI :10.1016/j.electacta.2012.09.115
5. Li-S batteries: simple approaches for superior performances, Rezan Demir-Cakan,
Mathieu Morcrette, Gangulibabu, Aurélie Guéguen, Rémi Dedryvère and JeanMarie Tarascon, Energy Environ. Sci. 6 (2013) 176
List of Publications on closely related R & D
1. CAM sol-gel synthesized LiMPO4 (M=Co, Ni) cathodes for rechargeable
lithium batteries, Gangulibabu, D. Bhuvaneswari, N. Kalaiselvi, N. Jayaprakash, P.
Periasamy, J. Sol Gel Sci Technol 49 (2009) 137
2. Feasibility studies on newly identified LiCrP2O7 compound for lithium
Insertion behavior, Gangulibabu, D. Bhuvaneswari, N. Kalaiselvi, Applied
Physics A-Material science and Processing 96 (2009) 489
3. A new class of Sol-gel derived LiM1xM2yMn2-x-yO3.8F0.2 (M1=Cr, M2=V;
x=y=0.2) cathodes for lithium batteries, N. Jayaprakash, N. Kalaiselvi, C. H.
Doh, Gangulibabu, D. Bhuvaneswari, J. Appl. Electrochem. 40 (2010) 2193
4. H2O2 aided one-pot hydrothermal synthesis of nanocrystalline LiMn2O4
cathode for lithium batteries, K. Sathiyaraj, Gangulibabu, D. Bhuvaneswari,
171
N. Kalaiselvi and A. John Peter, IEEE Transactions on Nanotechnology 11
(2011) 314
5. Effect on reaction temperature on morphology and electrochemical behavior
of LiCoO2, K. Sathiyaraj, Gangulibabu, D. Bhuvaneswari, N. Kalaiselvi,
Ionics 17 (2011) 49
6. Effect of mono-(Cr) and bication(Cr, V) substitution on LiMn2O4 spinel
cathodes, N. Jayaprakash, N. Kalaiselvi, Gangulibabu, D. Bhuvaneswari, J.
Solid State Electrochem. 15 (2011) 1243
7. Role of iron dopant and carbon additive in improving the ionic transport and
electrochemical properties of LiFexMn1−xPO4 (x=0.25 and 0.75) solid solutions,
D. Bhuvaneswari, Gangulibabu, C. H. Doh, N. Kalaiselvi, Int. J.
Electrochem. Sci., 6 (2011) 3714
8. Li3MxV2-x(PO4)3/C (M=Fe, Co) composite cathodes with extended solubility
limit and improved electrochemical behavior, K. Nathiya, D. Bhuvaneswari,
Gangulibabu, D. Nirmala, N. Kalaiselvi, RSC Advances 2 (2012) 6885
9. Temperature – Dependent surface morphology kinetics of LiCoO2 cathode
synthesized using combustion method, R. Lakshmanan, Gangulibabu, D.
Bhuvaneswari, N. Kalaiselvi, Metals and Materials International 18 (2012)
249
10. Surfactant coassisted sol-gel synthesis to prepare LiNixMnyCo1-2yO2 with
improved electrochemical behavior, D. Bhuvaneswari, Gangulibabu, N.
Kalaiselvi, J. Solid State Electrochemistry (Article in Press) DOI
10.1007/s10008-012-1810-8
11. Combustion synthesized nanocrystalline Li3V2(PO4)3/C cathode for lithium
batteries, K. Nathiya, D. Bhuvaneswari, Gangulibabu, N. Kalaiselvi,
Materials Research Bulletin – 47 (2012) 4300
Papers Presented at National/International Conferences
1. CAM sol-gel synthesized LiMPO4 (M=Co, Ni) cathodes for lithium battery
applications, Gangulibabu, D. Bhuvaneswari and N. Kalaiselvi, International
Conference on Electrochemical Power Systems (ICEPS-3), (November 26–28,
2008: Mascot Hotel, Thiruvananthapuram, Kerala, India) - POSTER
172