THESIS
2014
xiv, 76 pages : illustrations ; 30 cm
Abstract
Lithium ion batteries (LIBs) are the most popular energy storage devices nowadays
and have shown great potentials in the applications in electric vehicles and energy
storage systems for sustainable energies such as wind and solar power. However, the
organic electrolytes are of high flammability and might cause safety hazards if used
improperly. Moreover, they are expensive due to the costs of the organic solvents and
the critical synthesis conditions required for the lithium salts. On the contrary, LIBs
based on aqueous electrolyte are superior to the ones based organic electrolyte in
terms of safety and cost. In particular, LiTi
2(PO
4)
3 is an ideal candidate as an anode
material for aqueous LIBs considering its suitable Li
+ insertion and extraction potential and acceptable capac...[
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Lithium ion batteries (LIBs) are the most popular energy storage devices nowadays
and have shown great potentials in the applications in electric vehicles and energy
storage systems for sustainable energies such as wind and solar power. However, the
organic electrolytes are of high flammability and might cause safety hazards if used
improperly. Moreover, they are expensive due to the costs of the organic solvents and
the critical synthesis conditions required for the lithium salts. On the contrary, LIBs
based on aqueous electrolyte are superior to the ones based organic electrolyte in
terms of safety and cost. In particular, LiTi
2(PO
4)
3 is an ideal candidate as an anode
material for aqueous LIBs considering its suitable Li
+ insertion and extraction potential and acceptable capacity. However, currently it suffers from the poor rate
performance due to its low electrical conductivity and severe capacity fading when
cycled in aqueous electrolyte.
In this thesis, a one-pot sintering process incorporating sol-gel preparation route
and in-situ carbon coating for the synthesis of carbon coated submicron-sized
LiTi
2(PO
4)
3 was proposed to overcome the aforementioned drawbacks of typical
LiTi
2(PO
4)
3 particles. Experimental results showed that the carbon content,
calcination temperature and concentration of Ti
3+ have significant impacts on the
electrochemical performance of the as-prepared carbon coated LiTi
2(PO
4)
3 particles in
both organic and aqueous electrolytes. It was found that carbon coated LiTi
2(PO
4)
3
particles obtained with 60 wt% pitch addition (about 9.5% carbon coated) and
calcined at 850 °C for 12 h show the highest capacity of 110 mAh g
-1 when cycled at
10 C in organic electrolyte comparing with other synthesis conditions. The
rhombohedral crystal structure (space group R3c) and phase purity of the as-prepared
carbon coated LiTi
2(PO
4)
3
were confirmed by XRD analysis. The particles are of
300~500 nm in diameter and interconnected by carbon coating (3~5 nm in thickness).
The carbon coated LiTi
2(PO
4)
3
exhibits an initial specific capacity of 103 mAh·g
-1
and retains 80.6% of the initial capacity after 120 cycles in 2 M Li
2SO
4 aqueous
electrolyte at 1 C rate. Even at 10 C, the composite can still deliver 90 mAh g
-1 with
67.7% capacity retention after 1000 cycles. The high rate performance and excellent
cycling life of LiTi
2(PO
4)
3 in aqueous electrolyte reveal its potential as negative
electrode in aqueous lithium ion batteries for electric vehicles and industrial-scale
energy storage.
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