Studies On Synthesis And Coating Modification Of Na_1.1V₃O₇.9 As Anode Materials Of Aqueous Lithium-ion

Nowadays, the organic lithium ion batteries with high capacity, long life, light weight and strong power storage have been widely used in portable electronic devices.However, certain drawbacks such as high cost, safety issues at abuse conditions and rigorous assembling requirements have greatly limited the further development.Compared with the organic lithium ion battery, aqueous rechargeable lithium battery（ARLB） has many advantages such as low cost, safe, simple assembly conditions and environmentally friendly. It is considered to be one of the most novel electrochemical power sources. Due to the norrow theoretical stable range of aqueous electrolyte, it needs the charging and discharging platform of electrode material in electrolyte decomposition voltage range. The cathode materials in ARLB are relatively more than anode material. Therefore, the development of ARLB is limited primarily by the anode electrode material. This papepr is focused on the anode electrode material of ARLB and the main results are listed as below:1. Na_1.1V₃O_7.9 has many advantages such as high specific capacity, excellent structural stability and excellent cycling performance. It is considered to be one of the most promising anode material for ARLB. In this paper, sodium vanadate precursor（name as NVO） was synthesized by one-step hydrothermal reaction. Subsequent,Na_1.1V₃O_7.9 was obtained by the various calcination temperatures（name as N300,N350 and N400）. the morphology and structure of N300, N350 and N400 were characterized by scanning electron microscopy（SEM） and X-ray diffraction（XRD）,The results showed that N300, N350 and N400 were nanorods and layered monoclinic structure. The electrochemical properties of Na_1.1V₃O_7.9 in saturated lithium nitrate（LiNO₃） have been characterized by cyclic voltammetry（CV）, galvanostatic charge/discharge experiments and electrochemical impedance spectroscopy（EIS）,The electrochemical behaviors of N300, N350 and N400 in saturated LiNO₃ solution were compared, The results showed that nanorods N300 obtained best electrochemical performance of the highest specific capacity, the best electrochemical cycling stability and the least impedance. The initial discharge capacity of N300 at current density of300 mAg^-1, 500 mAg^-1, 1000 mAg^-1 and 1500 mAg^-1 was 130 mAh g^-1, 115 mAh g^-1,114 mAh g^-1 and 93 mAh g^-1, respectively. After 200 cycles, the corresponding capacity retention was 62%, 64%, 55% and 65%, respectively. However, Na_1.1V₃O_7.9electrochemical performance in saturated solution of LiNO₃ needs further improvement.2. Na_1.1V₃O_7.9 was used as the substrate, and the conductive polymer PPy was coated. The morphology and structure of Na_1.1V₃O_7.9@PPy were characterized by SEM and XRD, the results showed that Na_1.1V₃O_7.9@PPy did not change morphology and structure of Na_1.1V₃O_7.9. The electrochemical properties of Na_1.1V₃O_7.9@PPy in saturated LiNO₃ solution were characterized by CV, galvanostatic charge/discharge and EIS experiments. The electrochemical behaviors of Na_1.1V₃O_7.9@PPy with different coated time in saturated LiNO₃ solution were compared. The results showed that Na_1.1V₃O_7.9@PPy with 12 h coated time obtained best electrochemical performance. The initial discharge capacity of Na_1.1V₃O_7.9@PPy with 12 h coated time at current density of 300 mAg^-1,1000 mAg^-1 and 5000 mAg^-1 was 193 mAh g^-1,166 mAh g^-1and 143 mAh g^-1, respectively. After 200 cycles, the discharge capacity was 126 mAh g^-1,101 mAh g^-1 and 82 mAh g^-1, respectively. The corresponding capacity retention was 65%, 61% and 57%. The discharge capacity of Na_1.1V₃O_7.9@PPy is higer than pure Na_1.1V₃O_7.9.3. Na_1.1V₃O_7.9 was used as the substrate, and Al₂O₃ was coated. The morphology and structure of Na_1.1V₃O_7.9@Al₂O₃ were characterized by scanning electron SEM and XRD, the results showed that the length of Na_1.1V₃O_7.9@Al₂O₃ became short. The electrochemical properties of Na_1.1V₃O_7.9@Al₂O₃ in saturated LiNO₃ so lution were characterized by CV, galvanostatic charge/discharge and EIS experiments. The electrochemical behaviors of Na_1.1V₃O_7.9@Al₂O₃ with different coated amount in saturated LiNO₃ solution were compared. The results showed that Na_1.1V₃O_7.9@Al₂O₃with coated 3 wt% Al₂O₃ obtained best electrochemical performance. The initial discharge capacity of Na_1.1V₃O_7.9@Al₂O₃ with coated 3 wt% at current density of1000 mAg^-1 was 145 mAh g^-1, the discharge capacity was 135 mAh g^-1 after 2 cycles,115 mAh g^-1 after 50 cycles, 109 mAh g^-1 after 100 cycles and 105 mAh g^-1 after 200 cycles, respectively. The corresponding capacity retention was 72%. Comparing pure Na_1.1V₃O_7.9, the cycle performance of Na_1.1V₃O_7.9@Al₂O₃ has improved significantly.