锂离子电池正极材料磷酸钒锂的制备及其改性研究

发布时间：2018-04-04 22:31

本文选题：锂离子电池　切入点：镁掺杂　出处：《湘潭大学》2014年硕士论文

【摘要】：单斜结构的Li3V2(PO4)3材料因其具有高理论容量、高锂离子扩散率、优异的热稳定性和较好的循环稳定性，而成为最有潜力的锂离子电池正极材料。然而，，较低的电子电导率（2.010-8S cm-1）成为阻碍LVP发展的致命缺陷。因此，提高LVP材料的电子迁移率和离子迁移率是改善其电化学性能的有效对策。为了克服LVP材料的上述缺点，本论文通过改进合成方法和对LVP材料进行锂位金属离子掺杂等手段提高其电化学性能。在本论文中分别合成了Li3V2(PO4)3/C、Li3-2xMgxV2(PO4)3/C(x=0、x=0.01、x=0.03和x=0.05)和Li3-3xMgxNaxV2(PO4)3/C(x=0、x=0.03、x=0.05和x=0.07)复合材料。通过扫描电镜(SEM)、X-射线衍射(XRD)、电子衍射光谱(EDS)、交流阻抗(EIS)以及循环伏安(CV)和恒电流充放电等电化学测试手段，研究最优合成条件、镁离子以及钠镁离子在锂位掺杂对材料电化学性能的影响规律，优化合成条件并确定锂位掺杂离子的最佳含量。采用溶胶凝胶法制备Li3V2(PO4)3/C复合材料，通过XRD、SEM、CV、EIS和恒流充放电等测试方法，研究焙烧温度、碳源及钒源对复合材料的物理性能及电化学性能影响规律，并优化合成条件，确定合成材料的最佳合成条件，即最佳焙烧温度为800℃，最佳焙烧时间为8h，最佳碳源为柠檬酸和最佳钒源为V2O5。以LiAc、NH4H2PO4、Mg(NO3)2·6H2O、30%(v/v)H2O2和柠檬酸为原材料，采用溶胶凝胶法合成Li3-2xMgxV2(PO4)3/C(x=0.01、x=0.03和x=0.05)复合材料,讨论不同镁含量在锂位掺杂对材料物理性能及电化学性能的影响。结果表明，在0.01≤x≤0.05范围内，LVP在锂位引入掺杂Mg2+的条件下，仍然维持其单斜结构，但掺杂样品的晶胞体积大于未掺杂样品。所有掺杂样品的电化学性能均优于未掺杂样品，其中，Li2.94Mg0.03V2(PO4)3/C具有最好的电化学性能。其在3.0-4.8V电压范围及0.1C充放电倍率的条件下，Li3V2(PO4)3/C材料的首次放电容量仅为170mAh g-1，而Li2.94Mg0.03V2(PO4)3/C材料的首次放电容量高达192mAh g-1。30次循环后Li3V2(PO4)3/C材料的放电容量仅为144mAh g-1，而Li2.94Mg0.03V2(PO4)3/C材料的放电容量为170mAh g-1，其容量保持率分别为85%和89%。采用循环伏安法测定材料的锂离子扩散系数，结果表明在锂位掺杂少量Mg2+可以显著提高锂离子扩散系数，扩散系数的增大有利于提高锂离子在活性材料颗粒中的扩散速率，从而有利于提高活性材料的电化学性能。以LiAc、NH4H2PO4、Mg(NO3)2·6H2O、NaNO3、30%(v/v)H2O2和柠檬酸为原材料，采用溶胶凝胶法合成Li3-3xMgxNaxV2(PO4)3/C(x=0、x=0.03、x=0.05和x=0.07)复合材料，研究钠镁离子在锂位共掺杂对材料电化学性能的影响规律。结果表明，所有掺杂样品的电化学性能均优于未掺杂样品，其中，Li2.85Mg0.05Na0.05V2(PO4)3/C具有最好的电化学性能。在3.0-4.8V电压范围及0.1C的充放电条件下，Li3V2(PO4)3/C材料的首次放电容量仅为170mAh g-1，30次循环后其容量保持率为85%， Li2.85Mg0.05Na0.05V2(PO4)3/C的首次放电容量为190mAh g-1，30次循环后其容量保持率为88%。采用循环伏安法测试锂离子扩散系数，结果表明，钠镁离子共掺杂材料的锂离子扩散系数均比未掺杂材料要高，，这可能是共掺杂提高材料电化学性能的主要原因
[Abstract]:Monoclinic Li3V2 (PO4) 3 materials because of its high theoretical capacity, high lithium ion diffusion rate, excellent thermal stability and good cycle stability, and has become the most promising cathode materials for lithium ion batteries. However, low electronic conductivity (2.010-8S cm-1) become a fatal flaw hindering the development of LVP. Therefore, to improve the electron mobility of LVP materials and ion mobility are effective measures to improve its electrochemical performance. In order to overcome the disadvantages of LVP materials, this paper improved the synthesis methods and materials of LVP lithium metal ions doped in a better electrochemical performance. The Li3V2 were synthesized in this paper (PO4 3/C), Li3-2xMgxV2 (PO4) 3/C (x=0, x=0.01, x=0.03 and x=0.05) and Li3-3xMgxNaxV2 (PO4) 3/C (x=0, x=0.03, x=0.05 and x=0.07) composite materials. By scanning electron microscopy (SEM), X- ray diffraction (XRD), electron diffraction spectroscopy (EDS), AC Impedance (EIS), cyclic voltammetry (CV) and galvanostatic charge discharge method were used to study the optimal synthesis conditions, the influence of magnesium ion and sodium magnesium ion on the electrochemical performance of lithium doped materials, optimize the synthesis conditions and determine the optimum content of lithium doped ions.
Preparation of Li3V2 by sol gel method (PO4) 3/C composites by XRD, SEM, CV, EIS and galvanostatic charge discharge test method, the effects of calcination temperature, carbon source and vanadium source physical properties and electrochemical performance of composite materials, and optimize the synthesis conditions, determine the optimum conditions of the synthesis of materials synthesis that is, the best calcination temperature is 800 DEG C, the best roasting time is 8h, the best carbon source for citric acid and the best source of vanadium V2O5.
In LiAc, NH4H2PO4, Mg (NO3) 2 - 6H2O, 30% (v/v) H2O2 and citric acid as raw materials by sol gel method for synthesis of Li3-2xMgxV2 (PO4) 3/C (x=0.01, x=0.03 and x=0.05) composites, discussed different magnesium content in lithium doping on the physical properties of materials and electrochemical properties were studied. Results show that in x = 0.01 ~ 0.05 range, LVP introduced Mg2+ doped in lithium a condition, still maintain the monoclinic structure, but the cell volume is greater than the doped samples of undoped samples. The electrochemical properties of all doped samples are better than that of the undoped samples, among them, Li2.94Mg0.03V2 (PO4) 3/C has the best electrochemical performance. In the voltage range of 3.0-4.8V and the charge discharge rate of 0.1C under the condition of Li3V2 (PO4) 3/C materials and the initial discharge capacity is only 170mAh g-1, and Li2.94Mg0.03V2 (PO4) 3/C material for the first time a high discharge capacity of 192mAh after g-1.30 cycles of Li3V2 (PO4) 3/C discharge material Capacity is only 144mAh g-1 Li2.94Mg0.03V2 (PO4), and the discharge capacity of 3/C material is 170mAh g-1, the capacity retention rate was 85% 89%. and lithium ion diffusion coefficient were determined by cyclic voltammetry. The results show that the Li doped Mg2+ can significantly improve the lithium ion diffusion coefficient, diffusion coefficient increases in favor of improve the diffusion rate of lithium ion in the particles in the active material, which helps to improve the electrochemical performance of the active material.
In LiAc, NH4H2PO4, Mg (NO3) 2 - 6H2O, NaNO3,30% (v/v) H2O2 and citric acid as raw materials by sol gel method for synthesis of Li3-3xMgxNaxV2 (PO4) 3/C (x=0, x=0.03, x=0.05 and x=0.07) composite materials, research of sodium magnesium ion in Li Co doped on the electrochemical properties of materials were investigated. The results show that the electrochemical properties of all doped samples are better than that of the undoped samples, among them, Li2.85Mg0.05Na0.05V2 (PO4) 3/C has the best electrochemical performance. The discharge conditions and the voltage range of 3.0-4.8V 0.1C, Li3V2 (PO4) 3/C materials the first discharge capacity is only 170mAh g-1,30 cycles, the capacity retention rate was 85% Li2.85Mg0.05Na0.05V2 (PO4) 3/C, the initial discharge capacity was 190mAh after g-1,30 cycles the capacity retention rate was 88%. by cyclic voltammetry of lithium ion diffusion coefficient, the test results show that the lithium magnesium sodium ion Co doped material diffusion coefficients Higher than undoped materials, this may be the main reason for CO doping to improve the electrochemical properties of the materials.

【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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