Font Size: a A A

Preparation And Electrochemical Li-Absorption/Extraction Behavior Of Some Nanometric Sb-Based Intermetallic Compounds

Posted on:2006-11-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:J XieFull Text:PDF
GTID:1101360152471734Subject:Materials science
Abstract/Summary:PDF Full Text Request
One of the hotspots in the research of lithium-ion batteries is the development for the high-capacity and high-cycling-behavior anode materials to replace the conventional carbon-based materials. In the present work, some novel Sb-based intermetallic anode materials with high capacity are developed and their cycling stability is improved by applying nano-technology and composite-technology.Single phase skutterudite-structured CoSb3 intermetallic compound is prepared by two-step solvothermal method using CoCl2·6H2O, SbCl3 as the starting materials and NaBH4 as the reducing agent, namely, the solvothermal reactions are carried out at 190℃ for 24 h and are continued at 240℃ for another 48 h. CoSb2 formed at 190°C acts as the intermediate during the formation of CoSb3 as proved by XRD results. SEM and TEM observations show that the particle size of CoSb3 prepared by solvothermal method is 20 ~ 40 nm. Single phase CoSb2 and CoSb intermetallic compounds are prepared by solvothermal method at 190℃ and 220°C, respectively, using the same starting materials and reducing agent as that used in the synthesis of CoSb3. The particle size of both the compounds is in nanoscale. To avoid the use of expensive cobalt, Co-Sb compounds are replaced by their corresponding Fe-Sb and Ni-Sb compounds. Nano-Fe0.5Ni0.5Sb3, the counterpart of nano-CoSb3, and nano-FeSb2 and nano-NiSb2, the counterparts of nano-CoSb2, are prepared by solvothermal method using FeCl3·6H2O, NiCl2·6H2O, SbCl3 as the starting materials and NaBH4 as the reducing agent.The first Li-absorption/extraction capacities of nano-CoSb3 are 778 mA h g-1 and 521 mA h g-1, respectively. A reversible capacity of 391 mA h g-1 is still maintained after 20 charge and discharge cycles for this material. In contrast, the reversible capacity of micro-CoSb3, prepared by levitation-melting/ball-milling route, drops to 107 mA h g-1 after same cycle number. The first reversible capacities of nano-CoSb2 and nano-CoSb are 582 and 362 mA h g-1, respectively. Compared with the micro-CoSb2 and micro-CoSb, nano-CoSb2 and nano-CoSb exhibit significantly improved cycling stability. Nano-Feo.5Ni0.5Sb3 exhibits similar Li-absorption/extraction mechanism to nano-CoSb3. The first reversible capacity of this material reaches 559 mAh g-1 and a reversible capacity of 300 mA h g-1 is still maintained after 20 cycles. Similarly, nano-FeSb2 and nano-NiSb2 show similar Li-absorption/extraction mechanism to nano-CoSb2. The first reversible capacity of nano-FeSb2 reaches 523 mAh g-1 and a reversible capacity of 349 mA h g-1 is still maintained after 20 cycles, while the reversible capacity of micro-FeSb2 drops to 101 mAh g-1 after same cycle number. The first reversible capacity of nano-NiSb2 is 514 mA h g-1, and its cycling stability is somewhat improved compared to micro-NiSb2. It is found that small absolute volume changes occur for nanomaterials due to their small particle size and uniform particle distribution, which mitigate the pulverization and exfoliation of the particles, leading to slow capacity fade. In contrast, severe pulverization and exfoliation of the particles (especially for the sharp-angles and edges generated by ball-milling) occur for micromaterials due to the large absolute volume changes, causing rapid capacity fade.CoSb3/MCMB composite is prepared by high-energy ball milling. The first reversible capacity of this material reaches 721 mA h g-1, which is higher than its theoretical capacity, 550 mA h g-1. In addition, the composite shows improved cycling behavior compared to bare CoSb3. The improvement of its electrochemical performance can be attributed to the synergetic effect between CoSb3 and MCMB. CoSb3/MWNTs nanocomposites are prepared by in-situ solvothermal and mechanical milling methods, respectively. It is found that the composite prepared by in-situ solvothermal method shows rather better cycling stability compared to the one prepared by mechanical milling. This material combines the respective virtue of MWNTs and nano-CoSb3, namely, good cycling stability of MWNTs and l...
Keywords/Search Tags:Lithium-ion batteries, Anode material, Nanomaterial, Sb-based intermetallic compound, Solvothermal, Levitation melting, Electrochemical performance
PDF Full Text Request
Related items