【作者】 刘志明；

【导师】 王先友；

【作者基本信息】 湘潭大学 ， 物理化学， 2007， 硕士

【摘要】 在近年发展起来的可充电电池中,锂离子电池由于其优良的性能而在电子工业和电子产品中得到广泛的应用,如果能开发出具有更好电化学性能的钠离子电池,相对于锂离子电池来说,它将具有更多的优势,如它能明显地降低原材料的成本和能采用分解电压更低的电解液。因此,钠离子电池将是一种有前景的新型电池。本论文报道了用两段高温固相法制备NaVPO₄F作为钠离子电池正极材料,并用傅立叶红外光谱（FT-IR）,原子吸收（AAS）,热重分析（TG/DTG）,X-射线衍射（XRD）,扫描电镜（SEM）,恒流充放电,循环伏安,交流阻抗等对其结构和性能进行了测试和表征。结果表明:600℃左右反应可以获得结构稳定、结晶性好的NaVPO₄F,其晶型为简单单斜晶型。SEM测试表明NaVPO₄F的粒径分布均匀,其大小在微米级,材料首次放电容量为86.3mAh/g。循环伏安曲线中有两对氧化还原峰,和充放电曲线上出现的两个充放电平台一致。本论文在高温固相法合成NaVPO₄F的同时,掺杂Fe元素得到了NaV_1-xFe_xPO₄F（x=0-0.1）。红外光谱测试表明掺杂后的材料的振动吸收峰增强,Fe掺入越多,峰越往高波数方向移动,说明掺杂Fe可增强V-O键强度,掺杂Fe使材料的晶胞发生收缩,因此由于掺杂Fe元素,材料结构稳定性增加,循环性能更好。XRD测试证实了掺杂少量的Fe元素不影响材料的晶体结构,Fe成功地取代了V的位置得到了单相固溶体,掺杂Fe的量越多,吸收峰越锐利,峰强度越大,说明材料的结晶性能越好,电化学循环过程中材料的循环稳定性亦越好。掺Fe后的材料电化学循环稳定性得到较好的改善,其中NaV_0.96Fe_0.04PO₄F和NaV_0.94Fe_0.06PO₄F的首次放电容量分别为81.6mAh/g和74.5mAh/g,20次循环后的放电容量分别为66.7mAh/g和68.4mAh/g,而NaVPO₄F的首次放电容量为86.3mAh/g,20次循环后的放电容量为62.9mAh/g。本论文还通过高温固相法合成掺杂Al元素的NaV_1-xAl_xPO₄F（x=0,0.02）。红外光谱研究表明掺杂后的材料的振动吸收峰增强,掺杂Al后使材料的晶胞发生收缩,材料的结构稳定性增加,有利于循环稳定性的提高。XRD测试表明NaV_0.98Al_0.02PO₄F与NaVPO₄F具有相同的晶型,都为简单单斜晶型。SEM测试表明NaV_0.98Al_0.02PO₄F的粒径分布更加均匀,均匀的结晶有利于材料电化学性能的改善。电化学性能测试表明:掺入Al后的材料电化学循环稳定性得到较好的改善,NaVPO₄F的首次放电容量为86.3mAh/g,30次循环后的放电容量为50.4mAh/g,容量保持率为58.4%,NaV_0.98Al_0.02PO₄F的首次放电容量为80.4mAh/g,30次循环后的放电容量为68.3mAh/g,容量保持率为85%。更多还原

【Abstract】 Lithium-ion batteries are currently one of the most popular types of rechargeable battery commonly used in consumer electronics. If sodium-ion rechargeable batteries with good performance characteristics could be developed, it would have some significant advantages over lithium-ion batteries, notably a reduction in raw materials cost and the ability to utilize electrolyte systems of lower decomposition （due to the higher half-reaction potential for sodium relative to lithium）. If so, sodium-ion batteries will be a kind of promising novel batteries.In this thesis, the cathode materials of sodium-ion battery, NaVPO₄F, were prepared under the protection of argon atmosphere by two step high temperature solid-state reactions. The structure and performance of as-prepared cathode material was characterized by Flourier-Infrared Spectra （FT-IR）, Atomic Absorption Spectra （AAS）, Thermogravimetric Analysis（TG/DTG）, X-ray Diffractometer （XRD）, Scanning Electron Microscope （SEM）, the galvanostatic charge/discharge, Cyclic voltammograms（CV） and Electrochemical Impedance Spectroscopy（EIS）. The results showed that NaVPO₄F with a good crystal stability can be obtained about a temperature of 600℃. Its crystal system was monoclinic. The SEM micrograph showed that the size of NaVPO₄F is micron-class, and the distribution of particle was uniform, the first discharge capacity of material was 86.3 mAh/g and the discharge capacity of NaVPO₄F was declined to 58.4%of its initial discharge capacity after 30 charge/discharge cycles.. The cyclic voltammogram showed two couples of peaks in cathodic sweep and anodic sweep. It agreed well with the two voltage plateaus of the curve of the charge/discharge curves for NaVPO₄F.In this thesis, NaV_1-x Fe xPO₄F （x=0-0.1） powders were synthesized with a high temperature solid state reaction. In the FT-IR spectrum of Fe doped materials, it was observed that the absorbance of peak increased comparing to the un-doped materials, and the band peak was moving to higher wave numbers as the doped amount of Fe increase. So, it explained that the strength of V-O band increased with the doped Fe, and the crystal cell shrunk. Moreover, it could be expected that the stability of materials would be enhanced and the cycle performance would be better with the introduction of Fe. The XRD results clearly confirmed that Fe substitution for V sites was successful and the single-phase solid solution was formed when the doped amount of Fe was increase to x=0.06. A small amount of Fe doping gave rise to the electrochemical cycling properties of NaV_1-x Fe xPO₄F. The as-prepared Fe-doped materials had a better cycle stability than the un-doped one, an initial reversible discharge capacity of NaV_0.96Fe_0.04PO₄Fand NaV_0.94Fe_0.06PO₄F are 81.6 mAh/g and 74.5mAh/g , respectively; the discharge capacity of NaV_0.96Fe_0.04PO₄F and NaV_0.94Fe_0.06PO₄F are 66.7 mAh/g and 68.4 mAh/g after 20 charge/discharge cycles. However, the first discharge capacity of NaVPO₄F is 86.3 mAh/g, the discharge capacity of NaVPO₄F is 62.9 mAh/g after 20 charge/discharge cycles.In addition, NaV_1-xAl_xPO₄F （x=0,0.02）powders were also synthesized with a high temperature solid state reaction. In the FT-IR spectrum of Al doped materials, it was observed that the absorbance of peak increased comparing to the un-doped materials, the crystal cell shrunk. So, it could be expected that the stability of materials would be enhanced and the cycle performance would be better with the introduction of Al. The XRD results clearly confirmed that the crystal phases of both samples are identified to be a monoclinic structure. The SEM results indicated that the Al doping sample had a smaller and uniform particle size than the un-doped sample; the electrochemical performance of the NaV_0.98Al_0.02PO₄F is known to be good, because the insertion and de-insertion of sodium ions during the charge and discharge processes can be facilitated when electrode materials are smaller in size. A small amount of Al doping gave rise to the electrochemical cycling properties of NaV_1-xAl_xPO₄F. The as-prepared Al-doped materials indicate a better cycle stability than the un-doped one. The initial reversible capacity of NaV_0.98Al_0.02PO₄F is 80.4 mAh/g,the discharge capacity of NaV_0.98Al_0.02PO₄F is 68.3mAh/g after 30 charge/discharge cycles, and the capacity retention at the 30th cycle is 85%.更多还原