Preparation Of Porous And Nano - Gap Cobalt Tetraxide And Its Application In Lithium Ion Batteries

In recent years, lithium ion secondary battery has become the fastest growing and most popular high-energy battery. It has a long cycle life, high energy, safety and no pollution, high operating voltage. And now, the graphite carbon anode materials have been commercialized, but its capacity （300-350 mA h g-1） is very lower and the capacity can not meet the requirements for fast charging. The theoretical capacity of the transition metal cobalt oxide （CoO, Co3O4） is 700-1000 mA h g-1, so people have done extensive researches on transition metal cobalt oxide as anodes for lithium ion battery. Current literature study mainly is to solve this problem in two ways:First, by the porous material or nano-gap to buffer volume effect, so that the electrolyte and electrode material are full of contact and the conductivity is enhanced; Second, using the carbon-based composite materials to promote the rapid transmission of electronic effects, and this method will buffer volume effect of the active material in the charging and discharging process. The main directions of this research is to study the synthesis of porous, nano-cobalt oxide material gap in order to improve the performance of lithium ion batteries.（1） The first time to use the inverse-opal SiO₂ as template, the inverse opal structure Co3O4 was prepared using the vertical deposition method and the spin coating method in two steps, and the amount of cobalt was adjusted by varying the number of spin coating. As the anode material in lithium-ion battery, these inverse-opal structure Co3O4 material is with high specific capacity and cycling performance, spin coating twice maintain at-900 mA h g-1, after the first spin coating maintain at -700 mA h g -1.（2） On the basis of the last chapter, we continue to use inverse opal SiO₂ as a template, combing with the first vertical deposition method and hydrothermal method study the presence or absence of SiO₂ inverse opal structure template for comparison electrochemical performance testing. The study found that the first cycle discharge capacity of stable straw-like CO3O4 is 1120 mAh g-1 at 0.5 C And the capacity retained 963 mA h g-1 after 100 cycles. Without SiO₂ inverse opal structure templates prepare urchin-like Co3O4, its initial discharge capacity is-1630 mA h g-1 at 0.5 C. And the capacity is-200 mA h g-1 after 100 cycles.（3） Using mesoporous SiO₂ as a template, taking the mesoporous SiO₂ onto precursor, mesoporous Co3O4 was prepared by high-temperature calcination. And then the different proportions graphene supported on mesoporous Co3O4 was synthesized by a conventional mechanical stirring,. This chapter explores the different proportions of the electrochemical properties of graphene mesoporous Co3O4 composite materials. The study found that when graphene supported on mesoporous Co3O4 composite at ratio of 1:5, the performance is the best. When the current density is 0.2 C, the capacity also maintains 700 mA h g-1 after 50 cycles.