Development And Application Of Electrode Materials And Devices For Sodium Ion Batteries

Due to the characteristics of low cost and rich sodium resources,sodium ion batteries,including organic and aqueous electrolytes,may be promising candidates in energy storage field.However,sodium-ion radius?1.06??is so large that sodium-ion cannot have a fast and reversible insertion-extraction in general material structure.For aqueous electrolytes,the theoretical decomposition voltage?1.23 V?window of water is narrow.These have greatly limited the selectivity of electrode materials for sodium ion batteries,especially for aqueous sodium ion batteries.So,the key to the application of sodium ion batteries is to find reversible sodium-ion insertion-extraction electrode materials with suitable potential and stable structure.The main research object of the article is the electrode materials of P2-type layered structure Na_0.67Ni_0.33Ti_0.67O₂ and NASICON structure NaTi₂?PO₄?₃.Through the small amount of Li-doping at the Ti site of Na_0.67Ni_0.33Ti_0.67O₂ and the three-dimensional carbon structure composited NaTi₂?PO₄?₃,the valence conversion efficiency and conductivity of electrode materials can be improved.On this basis,several sodium ion batteries have been studied in organic and aqueous electrolytes.The main contents and conclusions of the article are as follows:?1?NaNi_0.33Li_0.11Ti_0.56O₂ based symmetrical organic sodium ion batteries:a new O3-type layered compound NaNi_0.33Li_0.11Ti_0.56O₂ was obtained by Li-doped Na_0.67Ni_0.33Ti_0.67O₂.The conversion efficiency between Ni²⁺/Ni⁴⁺valences was improved by the introduction of lithium-ion,and the electrochemical performance of NaNi_0.33Li_0.11Ti_0.56O₂ electrode material as cathode was improved.The cyclic voltammetry curve analysis shows that the material NaNi_0.33Li_0.11Ti_0.56O₂ can be used as both positive electrode and negative electrode,which is called a bipolar electrode material.The mechanism of sodium-ion insertion of NaNi_0.33Li_0.11Ti_0.56O₂ electrode material was described by ex-situ XRD.And a new symmetrical organic sodium ion battery was assembled by NaNi_0.33Li_0.11Ti_0.56O₂ electrode material as both positive electrode and negative electrode.The working voltage of the battery is 3.1 V and the energy density is 100 Wh kg^-1.?the energy density was calculated based on the total mass of active electrode materials and the same below??2?AC/NaTi₂?PO₄?₃ based aqueous sodium ion capacitor-battery:the three-dimensional carbon structure of NaTi₂?PO₄?₃ was designed by the point contact of acetylene black,the surface contact of graphite and the coating of the sphere surface of the organic PVA.The activated carbon with porous nanostructure and larger specific surface area was obtained through the high temperature graphitization.A new type of aqueous sodium ion capacitor-battery with the working voltage of1.15V was assembled by using three dimensional carbon composited NaTi₂?PO₄?₃ as negative electrode and activated carbon as positive electrode.The energy density of the capacitor-battery can reach 31.8 Wh kg^-1,which is more than 2 times that of AC/AC capacitor.At the same time,the capacity retention of AC/NaTi₂?PO₄?₃ based aqueous sodium ion capacitor-battery can still reach 84.9%after 2000 cycles.AC/NaTi₂?PO₄?₃ capacitor-battery with the colloidal electrolyte was assembled instead of aqueous solution,which effectively reduced the side reaction of water decomposition.The coulombic efficiency was increased significantly.?3?LiFePO₄/NaTi₂?PO₄?₃ based aqueous hybrid ion battery:LiFePO₄/C composite with uniform particle size and smooth sphericity was prepared via sol-gel method.The discharge capacity of LiFePO₄/C in aqueous solution is close to its theoretical specific capacity.The ion-insertion behaviors of LiFePO₄ and NaTi₂?PO₄?₃in the Li⁺/Na⁺mixed aqueous solution were studied.A new type of aqueous hybrid ion battery with the working voltage of 1.0 V was assembled by using three dimensional carbon composited NaTi₂?PO₄?₃ as negative electrode and LiFePO₄/C as positive electrode.And the energy density of LiFePO₄/NaTi₂?PO₄?₃ battery is up to55.8 Wh kg^-1.?4?Na_2/3Ni_1/3Mn_2/3O₂/NaTi₂?PO₄?₃ based aqueous sodium ion battery:a series of P2-type layered compounds Na_2/3Ni_xMn_1-xO₂ with flake shape,uniform particles and pure phase were prepared.The electrochemical performance of Na_2/3Ni_xMn_1-xO₂ in aqueous solution was studied systematically and the ion-insertion mechanism of Na_2/3Ni_1/3Mn_2/3O₂ was analyzed in detail.When lithium-ion is added into sodium sulfate solution,lithium ions will spontaneously insert into the layered structure of Na_2/3Ni_1/3Mn_2/3O₂ to form[LiO₄]tetrahedra,which can make the crystal structure stable and improve the cyclic stability of Na_2/3Ni_1/3Mn_2/3O₂.A new type of aqueous sodium ion battery has been assembled by using three dimensional carbon composited NaTi₂?PO₄?₃ as negative electrode and Na_2/3Ni_1/3Mn_2/3O₂ as positive electrode,which has two voltage platforms of 1.4 V and 1.05 V and the energy density of 42.1 Wh kg^-1.