Preparation And Properties Of Electrode Materials For Sodium Ion Energy Storage Devices

Sodium and lithium have similar physical and chemical properties and their reserves are widely distributed,so sodium-based energy storage systems are a very attractive research area.At present,more and more researchers are devoted to exploring suitable electrode materials to design and construct high-performance sodium-based energy storage systems/devices.Among them,the electrochemical performance of the sodium ion battery cathode material is determined by the characteristics of the phase structure.During the charge/discharge process,the change of phase occurs easily and the material structure collapses during the cycling,which affects the electrochemical performance.Therefore,the main work is focused on the doping or substitution of bulk phase elements in the material to weaken the phase transition and improve the structural stability of the cathode material for Sodium ion batteries.The metal ion hybrid capacitor combines a battery-type anode e and a capacitor-type cathode,and has both high energy density and high power density.The key to achieving the high performance of this hybrid capacitor device depends on:the anode and cathode materials have good electrochemical matching in both capacity and kinetic behavior.Based on the above research background,the research content of this thesis includes the following three aspects:(1)First,Na2CO3,NiO,TiO2 were used as precursors,and solid phase synthesis method was used to prepare O3-type Na0.8Ni0.4Ti0.6O2(NNT)series samples by adjusting the reaction time,reaction temperature and sodium content.The effects of different reaction time,reaction temperature and sodium content on electrochemical performance were studied.The electrochemical performance of the prepared sample is best when the temperature is 950?,the time is 20h,and the sodium content is 10%excess:when the current density is 0.2A g-1,its initial capacity is 78mAh g-1.After 200 cycle,the capacity retention rate is 53%,especially in the first few cycles,the Coulomb efficiency is close to 100%.(2)we use Na2CO3,NiO,Mn2CO3 and TiO2 as precursors,solid-phase synthesis was used to prepare Na0.8NixMn1-xO2 samples with different reaction conditions by adjusting the reaction time,reaction temperature,and Ni/Mn ratio.SEM,XRD and XPS analysis results show that the samples are composed of plate-like particles and have a lamellar structure,and it is conducive to the transmission of sodium ions.After doping Ti,a sample Na0.8Ni0.4Mn0.6O2-Ti is obtained,which has excellent electrochemical performance(Under the high current density of 1A g-1,it has an initial capacity of 80mAh g-1,300 cycles,and the capacity retention rate is 72%),In situ XRD was used to further study the reaction mechanism and crystal structure changes during the Na+insertion/extraction process during charge and discharge.The results show that the charge and discharge process is reversible.Then,the material was used as a positive electrode,and 3D carbon was used as a negative electrode to test the electrochemical performance of the full cell.The device circulates 500 cycle at 1A g-1 and the capacity retention rate is 65.8%.This shows that in addition to the excellent performance of the material in the half-cell system,the battery performance is also excellent in the full battery.(3)Carbon nanosheets(CNS)were prepared by chemical vapor deposition using Na2CO3 as template.The method is simple,convenientand environmentally friendly.The CNSs display disordered structure,larger interlayer spacing and high conductivity.The enlarged interlayer space facilitates the insertion/desertion of sodium ions into the CNS,which gives it good sodium storage properties.When used as a anode,CNSs exhibits a high capacity of 138 mAh g-1 at 10 A g-1(63%retention of the capacity at 0.05 A g-1)and excellent long-cycle stability(retaining 144 mAh g-1 at 10 A g-1 after 12500 cycles),Sodium ion hybrid capacitors(SIHCs)were constructed by using battery-type CNS as anode and capacitive activated carbon(AC)as cathode.This device can provide high energy density of 135 Wh kg-1 at 250 W kg-1,and the maximum energy density at 69 Wh kg-1,at the power output of 25 kW kg-1.After 4,000 cycles,the capacity retention rate was 71.8%.