【作者】 卓海涛；

【导师】 王先友；

【作者基本信息】 湘潭大学 ， 物理化学， 2006， 硕士

【摘要】 锂离子电池现在已经成为便携式电子装备的动力源泉,例如:手机,可携式摄像机,手提式电脑。如果能开发出具有更好的电化学性能的钠离子电池,相对于锂离子电池来说,它将有更多的优势,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（由于钠离子的半电池电位相对于锂离子要高）。因此,钠离子电池将是一种有前景的新型电池。本论文报道了在氩气保护下用两段高温固相反应法制备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℃左右反应可以获得稳定的、结晶性好的NaVPO₄F,其晶型为简单单斜晶系,与前驱体VPO4的晶型一致。SEM测试表明NaVPO₄F的粒径分布均匀,粒径大小在微米级,材料首次放电容量为87mAh/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平台一致。但是NaVPO₄F在30个充放电循环后的放电容量仅为首次的50%,因此要通过修饰和掺杂技术来提高它的性能。本论文通过高温固相法合成了NaVPO₄F,同时掺杂Cr元素得到了NaV_1-xCr_xPO₄F（x=0-0.1）。红外光谱表明掺杂Cr后的材料吸收振动峰增强,Cr掺入越多,峰越往高波数方向移动,说明掺杂Cr可增强V-O键强度,掺杂Cr使材料的晶胞发生收缩,因此由于掺杂Cr元素,材料结构稳定性增加,循环稳定性能更好。X射线衍射证实了直到x=0.08时少量Cr的掺杂不影响它的晶体结构,没有杂相存在,Cr成功地取代了V位得到了单相固溶体,掺杂Cr的量越多,吸收峰越锐利,峰强度越大,说明材料结晶性能越好,电化学循环过程中循环稳定性能越好。掺杂不同量Cr的正极材料放电比容量均在80mAh/g左右。掺入Cr后的材料电化学循环稳定性得到较好的改善,首次放电容量能达到83.3mAh/g,效率高达90.3%,而且循环20次后可逆容量保持率仍然有91.4%。当掺杂Cr的量增加时,可逆容量降低,库仑效率增加,其中NaV_0.96Cr_0.04PO₄F和NaV_0.92Cr_0.08PO₄F的可逆容量损失分别为12.5mAh/g和7.6mAh/g,容量保持率分别为82.2%和91.4%。本论文采用高温固相法制备了NaVPO₄F和LiVPO₄F,分别以这两种活性物质作为钠离子电池和锂离子电池的正极材料,制备了二次电池。结果表明,在充放电曲线上都出现两个平台,首次放电容量分别为87mAh/g和100mAh/g,20次后可逆放电比容量分别有64.5mAh/g和86mAh/g,与首次相比其容量损失分别达22.9mAh/g和14mAh/g,容量保持率分别为73.5%和86%。更多还原

【Abstract】 Lithium-ion rechargeable batteries are now well established as power sources for portable electronic equipments such as cellular phone, camcorder and laptop computer. 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 potential （due to the higher half-reaction potential for sodium relative to lithium）. 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 methods. The structure and performance of the 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 （CVs） 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, and it was in accord with VPO4 precursor. The SEM micrograph showed that the size of NaVPO₄F is micron-class, and the distribution of particle was uniform, The first charge and discharge capacity of material was 87mAh/g。The cyclic voltammogram showed two couples of peaks in cathodic sweep and anodic sweep. It agreeed well with the two voltage plateaus of the curve of the charge/discharge curves for NaVPO₄F.However, the discharge capacity of NaVPO₄F was declined to less than by 50% of its initial discharge capacity after 30 charge/discharge cycles. In this thesis, NaVPO₄F were synthesized with a high temperature solid state reaction, and Cr was doped into this material to prepare NaV_1-xCr_xPO₄F（x=0-0.1） powders. In the FT-IR spectrum of Cr 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 Cr increase. So, it explained that the strength of V-O band increased with the doped Cr, and the crystal cell shrunk. So that, it could be expected that the stability of materials would be enhanced and the cycle performance would be better with the introduction of Cr. The XRD results clearly confirmed that Cr substitution for V sites was successful and the single-phase solid solution was formed更多还原