Design And Properties Of Aqueous Mixed Ion Full Battery Based On NaTi₂?PO₄?₃ Anode Material

Compared with the batteries which used organic solvent as electrolyte,the aqueous battery used water solution which has better safety and economy,and the aqueous system electrolyte also has the characteristics of high ionic conductivity.Thus,aqueous battery has gradually attracted the attention of many researchers all over the world.At present,many researches focus on electrode materials much more than the matching and designing of full battery.However,actually what scientists did to improve the performance of electrode materials is really hoping to improve the performance of full battery.There are a lot of problems of single ion water battery?aqueous lithium-ion battery,aqueous sodium-ion battery,nickel hydrogen battery?such as cost much,low voltage,low specific capacity,etc.Nasicon type materials NaTi₂?PO₄?₃ has a stable open three-dimensional structure which will result in a good rate capacity and cycle stability in the process of charge and discharge performance.Also NaTi₂?PO₄?₃ has a potential at-0.82 V?vs Ag/AgCl?.There are lots of advantages of cathode material LiMn₂O₄ such as simple preparation process,good rate capacity,low preparation cost and high charge/discharge potential.Also,Ni?OH?₂ has the advantages of good rate performance,great cycle stability and high charge/discharge capacity in alkaline system.In this thesis,NaTi₂?PO₄?₃was synthesized by solvothermal method and LiMn₂O₄ was synthesized by high temperature solid state method.Structure and morphology of the materials were analyzed by XRD,SEM,EDS,TG and other methods.Nasicon type material NaTi₂?PO₄?₃ is used as anode which is matched with different cathode?LiMn₂O₄,Ni?OH?₂?in mixed-ion electrolyte?0.5 mol/L Na₂SO₄+1 mol/L Li₂SO₄?0.1 mol/L NaOH+0.5 mol/L Na₂SO₄?to match the aqueous system mixed-ion full cell.Cyclic voltammetry,Constant current charge-discharge and other techniques were used to test the electrochemical performance of the materials and the full cell.The results are as follows:?1?Nano-sized NaTi₂?PO₄?₃ was successfully prepared by solvothermal method.Tartaric acid was used as carbon source and calcined together with NaTi₂?PO₄?₃ at high temperature under the protection of nitrogen to obtain different carbon contents?1.9%,4.8%,6.2%?NaTi₂?PO₄?₃/C composites;The electrochemical properties of NaTi₂?PO₄?₃/C composites with different carbon content were tested in0.5M Na₂SO₄ electrolyte.The results show that the NaTi₂?PO₄?₃/C composites have great electrochemical properties when the carbon content is 4.8%,at the current density of 132.8 mA g^-1,the charge and discharge capacity is 85.1 mAh g^-11 and 122.7 mAh g^-1,which shows a 69.3%coulombic efficiency.And the capacity retention is 65.5%after 100 cycles at the current density of 664 mA g^-1.?2?LiMn₂O₄ synthesized by high temperature solid state method has different morphologies at different sintering temperatures?700?,800?,900??.The result shows that the LiMn₂O₄ has the best morphology and cycle stability at the final firing temperature of 900?for 12 h.The discharge capacity of the first cycle reaches 80.5 mAh g^-11 at current density of 148 mA g^-1,and the capacity retention rate is 89.5%after 100 cycles.The mixed Li⁺/Na⁺full battery used LiMn₂O₄ as cathode and NaTi₂?PO₄?₃/C as anode material.Both of the materials were tested in 1 mol/L Li₂SO₄;0.5 mol/L Na₂SO₄+1 mol/L Li₂SO₄ and 0.5 mol/L Na₂SO₄ electrolyte.The results showed that Li⁺could de-intercalation/intercalation from/into LiMn₂O₄ but Na⁺could not because of its larger radius,and both ions?Li⁺and Na⁺?could intercalation/de-intercalation into/from NaTi₂?PO₄?₃ in which intercalation/de-intercalation peak potential of Li⁺and Na⁺is-0.82/-0.64 V?vs.SCE?,-0.95/-0.75V?vs.SCE?.Finally these materials were matched to a mixed ion battery according to the actual capacity.The average working voltage and energy density of the battery were up to 1.55 V and 59.3Wh kg^-11 at current density of 40 mA g^-1.And at current density of 80 mA g^-1,the capacity retention rate is 51.8%after 100 cycles.?3?Ni-MH battery has great capacity and good rate performance,but expensive anode material hydrogen storage alloy greatly limits its large-scale application.The electrochemical properties of commercial Ni?OH?₂/CoOOH and NaTi₂?PO₄?₃/C were tested in different electrolytes?6 mol/L NaOH;2 mol/L NaOH;0.1 mol/L NaOH+0.5 mol/L Na₂SO₄;0.01 mol/L NaOH+0.5 mol/L Na₂SO₄ and 0.5mol/L Na₂SO₄?.It was found that Ni?OH?₂ only reacted with OH^-.And as the concentration of OH^-decreases,the redox of Ni?OH?₂ moves forward.NaTi₂?PO₄?₃/C has the poor cycling performance in the mixed electrolyte containing OH^-but cycling performance becomes better with the decreasing concentration of OH^-.Ni?OH?₂/CoOOH and NaTi₂?PO₄?₃/C were matched to a full cell according to the actual specific capacity.The mixed ion full cell operated a working voltage of 1.1 V at the current density of 50 mA g^-1,and the energy density was 43.8 Wh kg^-1.After 50 cycles at the current density of 100 mA g^-1,the capacity retention rate was 42.6%.