Study And Modification Of Low Cost Cathode Materials In Sodium Ion Batteries

The rapid development of renewable energy,such as wind,solar and tidal power,has brought brightness to solve the fossil energy crisis.The application of secondary batteries in energy storage system has been regarded as a necessary method to solve the fluctuation of renewable energy.Lithium-ion batteries are not suitable for applications in energy storage due to their expensive price and resource short of lithium.Sodium-ion batteries have attacted much attention in recent years due to their low-cost and abundant resources.However,because of larger radius and heavier atomic mass,sodium-ion batteries have lower voltage platform and energy density compared with lithium-ion batteries.In hence,it is crucial to develop new electrode materials with high capacity and low cost.In this thesis,we have focused our interests on application of transit metal oxides as cathode in sodium-ion batteries.The content is as follows:V₂O₅ with various particle sizes and morphologies has been prepared.It was found that V₂O₅ nano-rods synthesized by ultrasonic method show better energy density and cycling performance.The energy density remains 278 m Wh g^-1 after 200 cycles at 50mA g^-1.During charge/discharge in the potential range of 1-4V,V₂O₅ suffers phase changes.The first irreversible phase transition occurred at 1.95V to new phase ofα’-Na V₂O₅.The second phase transition is reversible,occuring at the potential of 1.85V and 1.35V,respectively.By comparing the electrochemical performances of NaFeO₂ in different type of electrolytes,it concluded that NaFeO₂ has good electrochemical performance in ether electrolytes.The retention rate is 60% after 50 cycles.Besides,combined with resultscarbonate solvents,which causing fast fade of NaFeO₂ during cycling.The eletrochemical performance of R-MnO₂ in sodium-ion batteries has been studied.We found that R-MnO₂ could change to the phase of O’3-NaMnO₂ during the initial discharge.During the initial charge,O’3-NaMnO₂ would change into the phase of O₂.Then the subsequent reaction would proceed between these two phases.When using ionic liquid as electrolyte in R-MnO₂,the retention rate after 50 cycles increased to 75.9%.In addition,the retention rate could also be effectively improved after using sodium alginate as the binder instead of PVDF.