Research On The Synthesis And Modification Of NaTi₂?PO₄?₃ For Aqueous Sodium Ion Battery Cathode Materials

Environmental and resource problems are becoming more and more serious associated with traditional fossil energy consumption.Clean production and sustainable development become the main direction of the social and economic development.As an example,lithium-ion batteries in a portable power supply of new energy storage materials or devices have been widely used.Compared with lithium ions,sodium ion batteries have more advantages with its rich resources,low cost,security and stability,and environmental friendly in the field of large stationary energy storage.NASICON NaTi₂?PO₄?₃ have a typical structure,which is tunnel size allows sodium free migration.It showed a pair of symmetrical reversible REDOX peak corresponding to the embedded reversible reaction of sodium ions in cyclic voltammograms test.So sodium ion batteries are considered to be the best choice for the next generation of secondary batteries.In this work,NaTi₂?PO₄?₃ was synthesized and used as cathode material.At the same time,the modification and heat treatment effect on its electrochemical performance and structure were studied.The conclusions are as the following:Firstly,the cathode materials NaTi₂?PO₄?₃ was synthesized by solvothermal method.The pure NaTi₂?PO₄?₃ sample was obtained by hydrothermaling 24 hours and sintered at 650? for 2 hours.Compared with the literature,the sample had good crystal structure and morphology with less reunion,uniform particles and the best electrochemical performance.Specific capacity reached 60 mAh/g with flat potential plateau at 2C rate,which is much higher than the reference samples.The specific capacity was keeped especially at 40 mAh/g after 30 cycles.Secondly,NaTi₂?PO₄?₃ was modified with ascorbic acid as the carbon source.The heat treatment process was studied in the preparation of NaTi₂?PO₄?₃/C composite material by TG analysis.The optimization process was as follows: presintered at 400? for 3 hours,the heating rate of 2?/min;sintered at 650? for 2 hours,the heating rate of 2?/min.The results show that the sample had carbon content of 4% with better morphology,structure and good electrochemical performance.The first discharge specific capacity reached 150 mAh/g,which was remained to 118 mAh/g after 50 cycles recharge at 2C rate.The specific capacity had 108 mAh/g with flat potential plateau,which was remained to 91.8 mAh/g after 50 cycles at 5C rate.And the first discharge specific capacity reached 60 mAh/g,which was remained to 38 mAh/g after 300 cycles recharge at 20 C rate.It exhibits excellent cycling stability.At last,NaTi₂?PO₄?₃ was coated and modified by carbon and nitrogen with urea as carbon source.The C&N-NaTi₂?PO₄?₃ composite material were prepared through different heat treatment process.The results of optimization were as follows: presintered at 400? for 3 hours,the heating rate of 2?/min;Then sintered at 650? for 2 hours,the heating rate of 2?/min.The sample had carbon content of 4.3% with excellent morphology,structure and electrochemical performance.The first discharge specific capacity reached 141mAh/g,which was remained to 127.1 mAh/g after 30 cycles recharge at 2C rate.The specific capacity was 113mAh/g with flat potential plateau,which was remained to 97 mAh/g after 50 cycles at 5C rate.The specific capacity reached 78mAh/g,which was remained to 75.3 mAh/g of the capacity after 100 cycles at alternate 20 C.The C&N-NaTi₂?PO₄?₃ composite material exhibited excellent cycling stability.