Preparation And Modification Of Lithium/Sodium Titanium Phosphate Anode Materialds In Aqueous Ion Batteries

Aqueous ion batteries have received extensive attention from researchers due to the high ion conductivity,low raw material price,safety and environmental protection,and convenient assembly.LiTi2(PO4)3(LTP)and NaTi2(PO4)3(NTP)are promising anode materials in aqueous ion batteries because both LTP and NTP have fast ion conductors with a NASICON-type structure.The three-dimensional rigid framework inside is conducive to the diffusion of ions,but their electronic conductivity is poor and they are easily corroded by the electrolyte.Therefore,in this thesis,LTP and NTP were modified to further improve the electrochemical performance of LTP and NTP electrode materials and construct high-performance aqueous ion batteries.The research contents and results are as follows:(1)The LTP electrode was modified by the carbon coating.LTP/C composites were prepared through spray drying method followed by high-temperature calcination.The effects of the carbon coating on the electrochemical performance of LTP were explored.The results show that carbon coating can significantly improve the electronic conductivity and cycle stability of LTP.The amount of carbon coating and organic carbon sources on the electrode performance of LTP were also optimized.The optimal carbon coating amount and organic carbon source of LTP electrodes is 13%and polydopamine(PDA),respectively.The CC-LTP/PDA electrode with a carbon content of 13%has an initial discharge capacity of 127 mAh g-1 at a rate of 1 C,and the capacity decay rate is only 8%after 200 cycles.The first discharge specific capacity can still reach 112 mAh g-1 at a high rate of 5 C and the capacity retention rate reaches 86%after 1000 cycles.Besides,the soft pack battery were assembled with the prepared anode commercial lithium manganate cathode.The specific energy density of the 1 Ah soft pack battery can reach 50 Wh kg-1.(2)The NTP electrode was modified by Ca-doped.The NCaTP@C composite material was prepared by the sol-gel method.Ca doping broadens the Na+transfer path and improves the rate performance of the electrode.When the NCa0.02 TP@C sample is at a low rate of 1 C,the initial discharge specific capacity is 103.7 mAh g-1,and 82.9 mAh g-1 is retained after 100 cycles.The initial specific capacity of the NCa0.02TP@C sample can reach 89.9 mAh g-1 at a high rate of 5 C.(3)The NTP electrode was modified with carbon nano tube(CNT).NaTi2(PO4)3@C composites were prepared through spray drying method followed by high-temperature calcination.The effect of pure carbon layer coating and carbon layer and carbon nanotube co-coating on the structure and electrochemical performance of NTP were explored.The results show that the surface of the CNT-NTP@C electrode co-coated with carbon layer and carbon nanotubes can form a conductive network,which could accelerate the electron migration rate and further improve its electronic conductivity.The initial specific capacity of the 0.5%CNT-NTP@C electrode can reach 85 mAh g-1 at a high rate of 5 C,and the capacity retention rate is about 71%after 1000 long cycles.