Studies On Negative Materials In Aqueous Batteries

Nonaqueous sodium ion batteries（NIBS）have recently been investigated as a potential alternative to lithium ion batteries（LIBS）.The low cost of Na,its abundance compared to Li,and the similarity of its electrochemistry to that of LIBs all favor NIBs for large-scale applications,such as ESSs.NIBs based on aqueous electrolytes have the benefit of using Na as a charge carrier,as well as several advantages for use in large-scale applications.As previously discussed for ARLBS,an aqueous electrolyte is inherently safe and environmentally benign and can achieve higher power than organic electrolytes.In addition,from a practical aspect,ARSBs can be more cost-effective in that the water and Na salts used in aqueous systems such as Na2SO4,NaCl,and NaNO3 are inexpensive due to their natural abundance.In this section,we review recent progress on ARSBs with a focus on the development of active materials.In this paper,aqueous sodium ion batteries anode materials NaTi₂（PO₄）₃ and NaTi₂（PO₄）₃/C were prepared by sol-gel method.The structural analysis of the materials and the electrochemical performance of the materials were carried out by means of characterization.The effects of different proportions of magnesium dopants on their structure and electrochemical properties were studied.The details are as follows:Firstly,NaTi₂（PO₄）₃ material was prepared by sol-gel method,and then NaTi₂（PO₄）₃/C material was synthesized by the combination with organic carbon source.The electrochemical test results show that NaTi₂（PO₄）₃/C material shows better capacity and cycle performance.In the voltage range of-1.0 V ^-0.2 V,the first discharge specific capacity at 200 mA·g-1 current density is 101.5 mAh·g-1,the capacity loss after the first cycle is larger,then the capacity tends to be stable,and the discharge capacity after 50 cycles is 19.4 mAh·g-1.The discharge capacity of NaTi₂（PO₄）₃ material is only 48.3 mAh·g-1,accounting for 47.6% of the specific capacity of NaTi₂（PO₄）₃/C material,and the discharge capacity is 8.2 mAh·g-1 after 50 cycles.Its capacity retention rate of 17%,lower than the NaTi₂（PO₄）₃/C material 19%.Secondly,NaTi₂（PO₄）₃/C materials with Mg content of 2%,5%,8%,11% and 14% respectively were prepared by sol-gel method.The different contents of NaTi₂（PO₄）₃/C materials are tested for characterization and electrochemical performance.XRD shows that the structure of the materials are not changed greatly.Cyclic voltammetry（CV）shows that 5% and 8% of NaTi₂（PO₄）₃/C materials are more distinct,the rate cycle profile can also be seen 5% and 8% of the proportion of magnesium content of NaTi₂（PO₄）₃/C material possess the higher specific discharge capacity,and the materials in the cycle are relatively stable,charge and discharge efficiency are also higher.