Li3V2(PO4)3 nanocrystals embedded in a nanoporous carbon matrix supported on reduced graphene oxide sheets as cathode material for lithium-ion batteries

• Main Author: Wong, Kang Ming.
• Other Authors: School of Materials Science and Engineering
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: http://hdl.handle.net/10356/48409
• Institution: Nanyang Technological University

In this project, monoclinic Li3V2(PO4)3 (LVP) nanocrystals embedded in a nanoporous carbon matrix attached to reduced graphene oxide (rGO) nanosheets (LVP-NC@NPCM@rGO) are synthesized by a sol-gel method using NH4VO3, CH3COOLi∙2H2O, NH4H2PO4, citric acid and graphene oxide (GO) as starting materials. The structure and morphology of the samples were characterized by FESEM, TEM, XRD, Raman spectroscopy, TGA and nitrogen adsorption-desorption isotherms. The results reveal that 20-80 nm nanoparticles, consisting of 5-8 nm monoclinic LVP nanocrystals, embedded in a nanoporous carbon matrix with pore sizes of around 4 nm and attached to rGO nanosheets are successfully synthesized. In addition, the LVP-NC@NPCM@rGO exhibits high specific surface area which allowed it to be further fabricated into binder-free cathodes. The electrochemical measurements show that the LVP-NC@NPCM@rGO cathode displays excellent Li storage capabilities. In the voltage window of 3 to 4.3 V and at a current density of 66 mA g-1 (0.5 C), this cathode depicts an initial discharge capacity of 128 mAh g-1 (theoretical: 130 mAh g-1) and also displays excellent cycling stabilities with almost no capacity fading when subjected to 100 cycles of charging and discharging. In addition, even at high current density of 6600 mA g-1 (50 C), it is still able to deliver a constant discharge capacity of 88 mAh g-1 for 1000 cycles. In the voltage window of 3 to 4.8 V and at a current density of 40 mA g-1 (0.2 C), the cathode exhibits an even higher initial charge capacity of 181 mAh g-1, contributed by the extraction of the third Li+ at 4.6 V, which gradually decreases to 164 mAh g-1 during the 100th cycle and this is better than the performance that was ever reported for LVP-based cathodes. On top of that, the cathode is able to display excellent cycling performance and deliver a discharge capacity of 91 mAh g-1 during the 1000th cycle even at high current density of 5910 mAh g-1 (30 C). Lastly, the reasons for the excellent electrochemical performance of the LVP-NC@NPCM@rGO cathode and the purposed formation scheme of hierarchical LVP-NC@NPCM@rGO nanoarchitectures are also discussed in the report.