Controllable Growth And Electrochemical Properties Of CO₃O₄ Micro\Nanostructures As Anode Materials And For Lithium Ion Batteries

Lithium ion batteries?LIBs? become the important energy storage devices due to the outstanding advantages of high energy density, good cycle performance, high output voltage and environment friendly. Co₃O₄ has been demonstrated to be a promising electrode material for LIBs, owing to its extremely high theoretical specific capacity?890 mAh g-1?, crystal field stablization energies, and stable discharge platform. The aim in this thesis is to improve the discharge specific capacity, cycle performance and rate capability of LIBs. The key point is to control the micro/nano-architectural and morphology of Co₃O₄ active material. Co₃O₄ materials with different morphologies and nanowires in-situ growing in Ni foam were fabricated by a hydrothermal growth with subsequent calcination. The samples were directly used as anode of the LIB. Their phase constitution, morphology, crystal structure and electrochemical properties were characterized by physical and electrochemical methods. The main research results are as follows:1. Co₃O₄ materials with different morphologies were synthesized using urea as precipitant and hexahydrate nitric acid cobalt as cobalt resourse. In addition, sodium chloride adjusted the ion environment of the solution. 3D hierarchical Co₃O₄ microspheres electrodes exhibited a high reversible discharge capacity, excellent rate capability and good cycling performance. The Co₃O₄ microspheres anode achieved a discharge capacity of 1228 mAh g-1 at 200 m Ag^-1 after 170 cycles. The rate performance showed that a very high capacity of 1407 mAh g-1 can be restored, when the current density changes from 3200 mAg^-1 to 200 mAg^-1, higher than the initial capacity. Even the same battery cycled at high as 3200 mAg^-1, the discharge capacity stabilized at 587 mAh g-1.2. Monodisperse Co₃O₄ nanosheets have been fabricated by changing the hydrothermal reaction time. The discharge capacity can maintain at 960 mAh g-1 at 400 mAg^-1 after 100 cycles. A high capacity of 1135 mAh g-1 can be recovered when the current density was reduced again from 2000 mAg^-1 to 200 mAg^-1.3. Co₃O₄ nanowires have been fabricated on Ni foam by in-situ hydrothermal growth followed by calcination. The cyclic voltammetry curves presented a pair of redox peak indicate that the oxidation reactions are completed step by step. When the sample was directly used as anode, reversible capacity of 612 m Ah g-1 can be obtained at 1000 m Ag^-1. The same battery was further cycled at 500 mAg^-1, the reversibly capacity increased and maintained at about 900 m Ah g-1. The rate performance showed that a high capacity of 1060 mAh g-1 can be recovered rapidly when the current density was reduced again from 1000 mAg^-1 to 200 mAg^-1.