| Sodium super ionic conductor(NASICON) structure type materials are considered as one of promising materials for organic electrolyte and other aqueous lithium/sodium ion batteries, due to their flexible charge/discharge voltage platform advantages, stable structure and good cyclic stability. However, the intrinsic poor electronic conductivity and electrochemical inertness for poly aninion, thus seriously hinder the lithium/sodium ion insertion/deinsertion in the three-dimensional frame structure, which limiting their use as electrode materials in high power batteries. In order to improve the electronic conductivity of LiTi2(PO4)3 and NaTi2(PO4)3, a series works are focus on solvothermal synthesis method and modification techniques. Ultimately, combining the advantages of carbon coating and design of microstructure, a better electrochemical performance of material is attained.Using ethylenediamine as chelating agent and carbon source, a porous carbon coated microplate LiTi2(PO4)3 were successfully synthesized by a facile solvothemal method. The results shows that amorphous carbon is uniformly coated on the edge of porous LiTi2(PO4)3 particles, thereby forming a layer of uniform conductive network, which effectively improves the electronic conductivity of the material. Porous structure is beneficial to the penetration of the electrolyte and the transfer of ions in the electrode materials. Electrochemical performance shows that the microplate structure of LiTi2(PO4)3(LTP/C) has a good electrochemical performance for organic lithium ion battery. In the voltage range of 1.5~3.5 V, LTP/C shows an initial discharge specific capacity of 121 mAh g-1 at 0.2 C rate, the capacity retention is 94.2% after 100 cycles. However, the pure LiTi2(PO4)3 materials only exhibits an initial discharge specific capacity of 106 mAh g-1 and remains at 65 mAh g-1 after 100 cycles.Furthermore, with the saturated LiNO3 solution as the electrolyte, the LTP/C as anode, and commercialized LiMn2O4 as cathode, a LTP/C//LiMn2O4 aqueous lithium ion battery was assembled. Within the voltage range of 0~1.8V, the LTP/C//LiMn2O4 cell is capable of providing an output voltage of 1.5 V. The LTP/C//LiMn2O4 cell shows the stable redox process, without causing the water electrolysis in the solution system. Under the different current densities of 20,50,100,200, and 1000 mA g-1, The cell can deliver a specific capacities of 76,67,64,56, and 34 mAh g-1, respectively. Finally,the aqueous lithium ion battery can obtain a considerable specific capacity.Using urea, triethyliamine, and ammonia as inducing agents, three types of NaTi2(PO4)3 with multilayered morphology plates were successfully synthesized by a simple solvothermal method. After mixing with glucose followed with the calcination process at high temperature, three tpyes of NaTi2(PO4)3/C(NTP/C) composites with special porous plate structure were formed. Nitrogen adsorption and desorption test shows that the NTP/C with ammonia as inducing agent possess a specific surface area of 79.8 m2 g-1, which is significantly higher than another two composites and better than urea and triethyliamine. The electrochemical performances of three types of NTP/C composites were tested in sodium ion batteries. Among these composites, NTP/C with the ammonia as inducing agent shows the highest discharge specific capacity, best rate performance, and cycle stability. Even at the high rate of 5 and 10 C, the material can still present discharge capacities of 95 and 85 mAh g-1, respectively. Besides the capacity retention is 86.3% and 82.3% after 120 cycles, respectively. |
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