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钠离子电池正极材料氟磷酸钒钠的低温制备 及性能探究
戚钰若
Subtype硕士
Thesis Advisor刘会洲 ; 赵君梅
2016-07
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline化学工程
Keyword钠离子电池 正极材料 Na3(Vo1-xpo4)2f1+2x (0≤x≤1) 低温溶剂热 低温水热
Abstract

随着可再生能源如太阳能、风能等的快速发展,迫切需要开发长寿命、低成本的储能电池。由于受到锂资源的制约,锂离子电池在大规模储能系统中的应用受到成本限制。作为同一主族的钠,与锂性质相似,且资源丰富,使钠离子电池在大规模储能领域的应用成为可能。Na3(VO1-xPO4)2F1+2x (0≤x≤1)是一类具有高稳定性、高放电电压、高放电比容量的钠离子电池正极材料。目前Na3(VO1-xPO4)2F1+2x (0≤x≤1)的合成方法主要为高温固相法(700-900 oC),具有能耗大的缺点,而正极材料的制备成本是储能电池成本的决定性因素。因此,用相对低温的溶液法来代替传统的高温固相法,是降低正极材料成本的重要手段。为此,我们提出了两种一步低温制备方法,即低温溶剂热和低温水热法。 首先,通过采用有机钒源,实现了Na3(VO1-xPO4)2F1+2x (0≤x≤1)的低温溶剂热合成(40-120 oC),并利用XRD、SEM、IR研究了系列化合物的结构差异。该方法所制备的材料具有优异的电化学性能:0.2C电流倍率下,储钠容量112 mAh?g-1、储钠电压3.75 V,在2C电流倍率下循环1200次后容量保持率为90%。其中,Na3(VOPO4)2F(x=0)样品具有突出的倍率性能,10C电流倍率下(6分钟充放电)的放电比容量为73 mAh?g-1,容量保持率为60%。 为进一步避免有机溶剂的使用,使合成体系更绿色,本论文开发了Na3(VO1-xPO4)2F1+2x (0≤x≤1)的低温水热合成法(120-220 oC)。本文以VCl3合成Na3(VPO4)2F3 (x=1)为代表,系统研究了四种磷源对产物形成的影响,证明pH值是能否成功合成出目标产物的关键因素,微酸性和中性环境更有利于产物的合成。通过调控合成体系的pH值或者采用不同的磷源、钒源,可以实现Na3(VO1-xPO4)2F1+2x (0≤x≤1)的可控合成。 本文提出的合成氟磷酸钒钠的方法,是以逐步降低能耗和使合成体系趋于绿色化为准则。与传统高温固相法相比,本文提出的低温溶液法显著降低材料制备成本,为该化合物的低温产业化制备奠定基础,并提供一种制备其它聚阴离子化合物的思路。

Other Abstract

With the rapid development of renewable energy sources, such as solar energy and wind energy, there is an urgent need to exploit energy storage batteries with long life and low cost. Restricted by limited lithium sources, the application of Li-ion batteries (LIBs) in large-scale energy storage systems has been limited by their cost. Na-ion batteries (SIBs) are becoming a potential alternative system for LIBs, because of their similar chemical properties and abundant sources of sodium. Na3(VO1-xPO4)2F1+2x (0≤x≤1) are a family of cathode materials for SIBs, with the merits of high structure stability, discharge voltage, and specific capacity. However, the high-temperature solid-state reaction, main synthetic method for this family of compounds, will undoubtedly increase the cost of materials production. In addition, it has been reported that materials production is the decisive factor of the total cost for producing an electrochemical storage system. Therefore, developing low-temperature solution methods to replace the traditional high-temperature solid-state method is an important way to reduce the cost of cathode materials. Hence, we develop two low-temperature routes, include low-temperature solvothermal method and low-temperature hydrothermal method. Firstly, a low-temperature solvothermal synthesis of Na3(VO1-xPO4)2F1+2x (0≤x≤1) in the temperature range of 40 to 120 oC has been realized by adopting organic vanadium sources. And the structural differences between them have been investigated using XRD patterns, SEM images, and IR spectroscopies. Both the Na3(VPO4)2F3 (x=1) and Na3(VOPO4)2F (x=0) demonstrate excellent electrochemical performance: a specific capacity of 112 mAh g-1 at a current rate of 0.2C with an average operation voltage of 3.75V, extraordinary cycling performance with 90% capacity retention over 1200 cycles at a 2C rate. Especially, the as-synthesized Na3(VOPO4)2F (x=0) nanoparticles show the best rate capability with a specific capacity of 73 mAh g-1 (60% capacity retention) at a 10C rate (6 min charge/discharge). Furtherly, a low-temperature hydrothermal method (120-220 oC) has been realized to completely avoid organic solvents and make the synthetic method more environmentally friendly. In this work, a systematical research has been made to investigate the influence of phosphorus sources on the crystallization of Na3(VPO4)2F3 (x=1), when using VCl3 as vanadium sources. The results show that pH is of great importance for the synthesis, and slightly acidic and neutral environment are benefical for the synthesis of Na3(VO1-xPO4)2F1+2x (0≤x≤1). Through controlling the pHs or matching vanadium sources and corresponding phosphorus sources, controlled synthesis of products of various crystallinity, morphologies, and sizes can be reached. In conclusion, these two methods were proposed following the guidelines of reducing cost and optimizing synthetic method. Compared with the conventional two-step high-temperature processes, these two solution routes would undoubtedly decrease the cost of material fabrication significantly, laying a foudation for the industrial production at lower temperature, and could be expanded as a general strategy for the synthesis of other polyanionic electrode materials.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/22929
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
戚钰若. 钠离子电池正极材料氟磷酸钒钠的低温制备 及性能探究[D]. 北京. 中国科学院研究生院,2016.
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