Recycling Of Waste LiFePO₄and Research Of Transition Metal Oxide Anode Materials

Lithium iron phosphate (LiFePO4), as a new lithium ion battery cathode material, has started industrialization. However, a new engineering problem-the recycling of waste LiFePO4will be raised as LiFePO4is widely used. In this thesis, a recycling method of LiFePO4with quenching technology has been brought up. In this method, the prepared LiFePO4has relatively good electrochemical performance. The specific capacity of recycled LiFePO4is almost150mAh/g in the first charge at0.1C current density. In addition, an easier and energy saving method has been used to recycle waste LiFePO4. In this method, it does not need to remove carbon and some polymers. Besides the recycling method of LiFePO4, this thesis also explored the preparing technology of LiFePO4by using iron oxide and ammonium dihydrogen phosphate as precursor. In the pilot production, the prepared LiFePO4is a pure phase, and the size of particles coated by carbon fiber is about100nm.In order to study the preparation of LiFePO4and improve electrochemical performance of carbon-coated iron oxide, iron oxides with variety of morphologies have been synthesized in this thesis. In this study, we use different concentration of ammonium dihydrogen phosphate and different reaction time to prepare iron oxide with different morphologies-nanotube, nanoring, nanorod. And we chose iron oxide nanotubes to be modified by designing carbon-coated structure. As a result, the length of the prepared Fe3O4/C composite with core-shell structure is300-600nm, and its diameter is less than100nm. and the thickness of carbon film is about5nm. The core-shell structure of Fe3O4/C will keep stable during charge and discharge process. Compared to Fe3O4, Fe3O4/C composite exhibits significantly improved electrochemical performance. After120cycles at current density of100mA/g, Fe3O4/C still keeps the capacity at about700mAh/g.This thesis attempts to utilize graphene (G) as three-dimensional conductive network to improve the electrochemical properties of nickel oxide (NiO) and NiO/graphene composite has been prepared. In this study, NiO particles are anchored on the graphene layers, and the graphene looks like three-dimensional network. In addition, the diameter of NiO particles is30-60nm, and its thickness is about5nm. The NiO particles are porous, which will improve its specific surface area. After60 cycles at100mA/g, NiO/graphene retains the specific capacity at about300mAh/g, while bare NiO just only has less than100mAh/g.