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, LiTi₂(PO₄)₃ is an ideal candidate as an anode material for aqueous LIBs considering its suitable Li⁺ insertion and extraction potential and acceptable capac...[ Read more ]

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, LiTi₂(PO₄)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 LiTi₂(PO₄)₃ was proposed to overcome the aforementioned drawbacks of typical LiTi₂(PO₄)₃ particles. Experimental results showed that the carbon content, calcination temperature and concentration of Ti³⁺ have significant impacts on the electrochemical performance of the as-prepared carbon coated LiTi₂(PO₄)₃ particles in both organic and aqueous electrolytes. It was found that carbon coated LiTi₂(PO₄)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 LiTi₂(PO₄)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 LiTi₂(PO₄)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 Li₂SO₄ 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 LiTi₂(PO₄)₃ in aqueous electrolyte reveal its potential as negative electrode in aqueous lithium ion batteries for electric vehicles and industrial-scale energy storage.