锂离子纳米阵列电极材料的制备及电化学性能研究

发布时间：2018-05-16 17:35

本文选题：磷酸铁锂 + 钛酸锂　；参考：《东南大学》2015年硕士论文

【摘要】：随着混合电动汽车的发展以及其对高能量密度和高功率密度储能器件的需求,锂离子混合超级电容器是近年来逐渐被关注的一种新型储能元件。锂离子混合超级电容器采用锂离子电池与超级电容器的电极材料,拥有锂离子电池和超级电容器电容的双重特性。与传统电容器相比,具有能量密度大的优良特性；与锂离子电池相比,具有功能以及功率密度高的优点。锂离子混合超级电容器的电极材料既包含具有电荷吸附活性的高比表面积的电容活性材料,又包含可与锂离子发生可逆脱嵌或氧化还原反应的电池材料,其能量存储过程既包含锂离子与电极材料体相发生的可逆法拉第化学反应,又包括电化学活性材料对锂离子的可逆吸脱附过程。本文研究了构成锂离子电容器的脱/嵌锂材料——磷酸铁锂和钛酸锂。磷酸铁锂与钛酸锂均具有低的导电性和低的Li+扩散系数的缺陷,这些缺陷限制了它们在大电流下实现快速充放电的可能。本文以提高锂离子电极材料的导电性,锂离子扩散系数,能量密度以及循环性能为目标,围绕如何能使在大电流下保持电极材料较高的比电容这一关键问题展开。一方面制备了具有纳米阵列形貌和结构的电极材料,另一方面通过电极材料本身改性,例如碳包覆,离子掺杂等来提高电极材料的导电性和锂离子扩散系数,使它们在较高的电流密度下也具有高的比容量,并且实现了快速充放电。采用SEM,XRD,Raman和EDS等方法分析了不同电极材料的形貌与结构,然后采用循环伏安法、充放电测试法以及交流阻抗法对不同的电极材料的电化学性质进行了测试和分析,本文的主要研究内容和结果如下。(1)碳包覆磷酸铁锂电极材料(C-LiFePO_4/TiN)的制备,形貌结构表征及其电化学性能的研究。基于对各种合成方法优缺点的比较,最后采用水热法合成了磷酸铁锂纳米颗粒,然后以蔗糖为碳源在氮气氛围下煅烧,形成碳包覆的磷酸铁锂(C-LiFePO_4)纳米颗粒。将C-LiFePO_4纳米颗粒原位沉积到氮化钛纳米线基底上,从而构建成碳包覆磷酸铁锂电极材料(C-LiFePO_4/TiN)。通过电化学测试,当电流密度为1 Ag~(-1)时,LiFePO_4/TiN与C-LiFePO_4/TiN纳米线电极材料的比电容分别为314 F g~(-1)和972 Fg~(-1)；当电流密度增加到20Ag~(-1), LiFePO_4/TiN与C-LiFePO_4/TiN纳米线电极材料的比电容分别为140Fg~(-1)和472.4 F g~(-1)。而且,LiFePO_4/TiN与C-LiFePO_4/TiN纳米线电极材料在电流密度为20Ag~(-1),循环400圈之后,比电容分别下降9.5%和3.7%,具有很好的大电流充放电性能和循环稳定性。交流阻抗显示,当开路电压为0.0V时,LiFePO_4/TiN与C-LiFePO_4/TiN纳米线电极材料的电荷转移电阻分别为0.3645ΩΩ和0.2512Ω,所对应的等效电路的电阻分别为5.447ΩΩ和2.678Ω；当开路电压为0.5V时,C-LiFePO_4/TiN纳米线电极材料的电荷转移电阻为0.2226Ω,所对应的等效电路的电阻为2.345Ω,表明引入高比表面积,高导电性的TiN作为基底材料,有助于提高材料的电化学性能;同时通过碳包覆可以有效提高材料本身的导电性,(2)碳包覆铁掺杂钛酸锂电极材料(C-Fe/Li_4Ti_5O_(12))的制备,形貌结构表征及其电化学性能的研究。采用阳极氧化钛片合成的二氧化钛为钛源,氢氧化锂为锂源,结合固液相反应法合成钛酸锂纳米管阵列材料,然后以硝酸铁为铁源,十二烷基硫酸钠为碳源合成了C-Fe/Li_4Ti_5O_(12)纳米管阵列电极材料。经过充放电测试,结果显示当电流密度为1A g~(-1)时,Fe/Li_4Ti_5O_(12)比电容为516F g~(-1)。当电流密度增加到10Ag~(-1)时,Fe/Li_4Ti_5O_(12)比电容为350F g~(-1)；当电流密度为1A g~(-1)时,Fe/Li_4Ti_5O_(12)比电容为768F g~(-1)。当电流密度增加到10A g~(-1)时,Fe/Li_4Ti_5O_(12)比电容为379F g~(-1),进一步表明,碳包覆可以有效提高电极材料本身的比电容。Fe/Li_4Ti_5O_(12)与C-Fe/Li_4Ti_5O_(12)在开路电压为0.5V下的Rct分别为14.1Ω和4.15Ω,可见由于碳的加入可以有效降低了Fe/Li_4Ti_5O_(12)本身的电荷转移电阻,提高了电极材料本身的导电性。Fe/Li_4Ti_5O_(12)与C-Fe/Li_4Ti_5O_(12)在0.5V时的Warburg阻抗分别为0.4869Ω和0.4183Ω,两者都具有更低的Warburg阻抗,因为Li_4Ti_5O_(12)本身呈现出阵列纳米管状结构,为电子转移提供了有效通道,使得离子扩散加快；而Fe3+嵌入到Ti4+位置为电子的迁移提供更多的空穴,使得更多的电子在Li4Ti5Oi2内部转移,导电性更强。而C-Fe/Li4Ti5Oi2具有更低的Warburg扩散阻抗,说明碳有效地包覆在了Fe/Li_4Ti_5O_(12)的表面,并且碳包覆加快了离子在电极和电解质之间传输过程。循环稳定性测试结果显示：为了验证该电极材料在大电流下充放电的稳定性,在10A g~(-1)下,500次循环测试,Fe/Li_4Ti_5O_(12)结果显示比电容下降了11.2%,C-Fe/Li4TisO12结果显示比电容下降了2.5%,相比Fe/Li_4Ti_5O_(12), C-Fe/Li_4Ti_5O_(12)电极材料的具有更好的循环稳定性。(3)氮掺杂钛酸锂(N-Li_4Ti_5O_(12))纳米线和纳米管阵列电极材料的制备,形貌结构表征及其电化学性能的研究。采用水热法合成了钛酸锂纳米线材料,采用阳极氧化的二氧化钛为钛源,氢氧化锂为锂源,固相-液相结合的方式合成钛酸锂纳米管状材料。然后将钛酸锂纳米线和钛酸锂纳米管材料进行氮掺杂,成功制备了N-Li_4Ti_5O_(12)纳米线和N-Li_4Ti_5O_(12)纳米管阵列材料。当电流密度为1 Ag~(-1)时,N-Li_4Ti_5O_(12)纳米线和N-Li_4Ti_5O_(12)纳米管的比电容分别为607.2 F g~(-1)和814.5Fg~(-1),当电流密度增加到20Ag~(-1)时,N-Li_4Ti_5O_(12)纳米线和N-Li_4Ti_5O_(12)纳米管的比电容分别为182.9Fg~(-1)和352F g~(-1)。在电化学交流阻抗测试中,在开路电压为0.5V下,N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管电极材料的电荷转移电阻为1.45Ω和0.147Ω,N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管电极材料交流阻抗谱在高频区显出半圆弧,并且在低频区呈现直线状态。N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管在开路电压为0.5V下的Rct分别为1.45Ω和0.147Ω,N掺杂可以有效降低了Li_4Ti_5O_(12)本身的电荷转移电阻,提高了电极材料本身的导电性。N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管在开路电压为0.5V时的Warburg阻抗分别为0.5463Ω和0.5135Ω,两者都具有更低的Warburg阻抗,N-Li_4Ti_5O_(12)纳米线本身呈现出纳米线阵列结构,而且线状结构中还包括介孔状结构,具有更大的比表面积,提高了活性物质的利用率；N-Li_4Ti_5O_(12)纳米管呈现出纳米管阵列结构,其特殊结构,不仅提高了电极材料本身的比表面积,而且为电子转移提供了有效通道,从而提高了电极材料的利用率,电子传输速率和锂离子扩散速率；同时N掺杂有效降低Li_4Ti_5O_(12)的禁带宽度,使得更多电子在Li_4Ti_5O_(12)内部转移,导电性更强。在电流密度为10A g~(-1)时,对N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管电极材料进行500次循环测试,N-Li_4Ti_5O_(12)纳米线与N-Li_4Ti_5O_(12)纳米管比电容分别下降了5.1%和1.6%,表示这两种电极材料均具有良好的电化学稳定性。
[Abstract]:With the development of hybrid electric vehicle and its demand for high energy density and high power density energy storage devices, lithium ion hybrid supercapacitor is a new type of energy storage element which has been paid more and more attention in recent years. Lithium ion hybrid supercapacitor uses lithium ion battery and supercapacitor electrode material, and has lithium ion battery and supercapacitor. Compared with the traditional capacitor, it has the excellent characteristics of large energy density compared with the traditional capacitor; compared with the lithium ion battery, it has the advantages of high function and high power density. The electrode material of the lithium ion hybrid supercapacitor contains both the capacitive active material with the high specific surface area with the charge adsorption activity, and it can also be contained in the lithium ion hybrid supercapacitor. A reversible redox or redox reaction of lithium ion battery material, the energy storage process includes both the reversible Faraday chemical reaction occurring in the phase of lithium ion and the electrode material, and the reversible desorption process of the lithium ion by the electrochemical active material. Iron lithium and lithium titanate. Both lithium phosphate and lithium titanate have low conductivity and low Li+ diffusion coefficient. These defects limit the possibility of fast charging and discharging at large current. This paper aims to improve the conductivity of the lithium ion electrode materials, the diffusion coefficient of lithium ion, the density of energy and the performance of circulation. On the one hand, the electrode materials with nanoarray morphology and structure are prepared. On the other hand, the modification of the electrode material itself, such as carbon coating and ion doping, improves the conductivity of the electrode materials and the lithium ion diffusion coefficient, so that they are higher. The current density also has high specific capacity, and the rapid charge discharge is realized. The morphology and structure of different electrode materials are analyzed by SEM, XRD, Raman and EDS. The electrochemical properties of different electrode materials are tested and analyzed by cyclic voltammetry, charge discharge test and AC impedance method. The main contents and results are as follows. (1) the preparation, morphology and electrochemical properties of carbon coated iron phosphate lithium-ion electrode material (C-LiFePO_4/TiN). Based on the comparison of the advantages and disadvantages of various synthetic methods, the nano particles of lithium iron phosphate are synthesized by hydrothermal method and then calcined in nitrogen atmosphere with sucrose as carbon source. Carbon coated iron lithium phosphate (C-LiFePO_4) nanoparticles. The C-LiFePO_4 nanoparticles are in situ deposited on the substrate of the titanium nitride nanowire, and the carbon coated lithium iron lithium electrode material (C-LiFePO_4/TiN) is constructed. By electrochemical testing, the electrochemistry of LiFePO_4/TiN and C-LiFePO_4/TiN Nanowire Electrode materials when the current density is 1 Ag~ (-1). The capacitance is 314 F g~ (-1) and 972 Fg~ (-1), and when the current density increases to 20Ag~ (-1), the specific capacitance of LiFePO_4/TiN and C-LiFePO_4/TiN Nanowire Electrode materials is 140Fg~ (-1) and 472.4 F. When the open circuit voltage is 0.0V, the charge transfer resistance of LiFePO_4/TiN and C-LiFePO_4/TiN Nanowire Electrode materials is 0.3645 omega and 0.2512 Omega respectively when the open circuit voltage is 0.0V. The resistance of the equivalent circuit is 5.447 omega and 2.678 Omega respectively. When the open circuit voltage is open, the impedance of the equivalent circuit is respectively 5.447 omega and 2.678 Omega. For 0.5V, the charge transfer resistance of the C-LiFePO_4/TiN Nanowire Electrode material is 0.2226 Omega, and the equivalent resistance of the equivalent circuit is 2.345 Omega. It shows that the introduction of high specific surface area and high conductivity TiN as the base material helps to improve the electrochemical performance of the material, and the carbon coating can effectively improve the electrical conductivity of the material itself, (2) carbon. The preparation, morphology and electrochemical properties of coated iron doped lithium titanate electrode material (C-Fe/Li_4Ti_5O_ (12)) were studied. Titanium dioxide was used as titanium source and lithium hydroxide was used as lithium source. The lithium titanate nanotube array materials were synthesized by the solid-liquid phase reaction method. Then iron nitrate was used as the iron source and twelve alkyl sulfur. C-Fe/Li_4Ti_5O_ (12) nanotube array electrode materials are synthesized as carbon sources. The results show that when the current density is 1A g~ (-1), the Fe/Li_4Ti_5O_ (12) specific capacitance is 516F g~ (-1). When the current density increases to 10Ag~ (-1), Fe/Li_4Ti_5O_ (12) is larger than capacitance. The O_ (12) specific capacitance is 768F g~ (-1). When the current density increases to 10A g~ (-1), Fe/Li_4Ti_5O_ (12) specific capacitance is 379F g~ (-1). It is further indicated that carbon coating can effectively increase the specific capacitance.Fe/Li_4Ti_5O_ (12) of the electrode material itself (12) and 4.15, respectively, under the open circuit voltage. It can effectively reduce the charge transfer resistance of Fe/Li_4Ti_5O_ (12) itself, improve the conductivity of the electrode material itself and the Warburg impedance of.Fe/Li_4Ti_5O_ (12) and C-Fe/Li_4Ti_5O_ (12) at 0.5V, respectively, 0.4869 omega and 0.4183 Omega, both of which have lower Warburg resistance, because Li_4Ti_5O_ (12) itself presents an array nanotubular junction. The structure provides an effective channel for electron transfer, which makes the ion diffusion faster; and the migration of Fe3+ into the Ti4+ position provides more holes for the migration of electrons, making more electrons transferred inside Li4Ti5Oi2 and more conductive. And C-Fe/Li4Ti5Oi2 has a lower Warburg diffusion impedance, indicating that carbon is effectively coated in Fe/Li_4Ti_5O_ (12). The surface, and the carbon coating accelerated the ion transmission between the electrode and the electrolyte. The cyclic stability test results showed that in order to verify the stability of the charge and discharge of the electrode material under the high current, the 500 cycle tests under 10A g~ (-1), the Fe/Li_4Ti_5O_ (12) result showed a 11.2% decrease in the specific capacitance, and the C-Fe/Li4TisO12 result showed the specific electricity. The volume decreased by 2.5%, compared with Fe/Li_4Ti_5O_ (12), C-Fe/Li_4Ti_5O_ (12) electrode material has better cyclic stability. (3) the preparation, morphology and electrochemical properties of nanowire and nanotube array electrode materials of nitrogen doped lithium titanate (N-Li_4Ti_5O_ (12)). The lithium titanate nanowire material was synthesized by hydrothermal method. Anodized titanium dioxide is the source of titanium, lithium hydroxide is a lithium source, and lithium titanate nanotube materials are synthesized by solid-phase liquid phase binding. Then, the N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotube arrays are prepared by doping lithium titanate nanowires and lithium titanate nanotube materials. The current density is 1 Ag~ (-1). The specific capacitance of N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotubes is 607.2 F g~ (-1) and 814.5Fg~ (-1) respectively. When the current density increases to 20Ag~ (-1), the specific capacitance of the N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotubes is respectively 182.9Fg~. The open circuit voltage is 0 in the electrochemical impedance test. Under.5V, the charge transfer resistance of N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotube electrodes is 1.45 omega and 0.147 Omega, N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotube electrodes show a semi circular arc in the high frequency region, and the linear state.N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) in the low frequency region are presented in the low frequency region. 12) the Rct of the nanotube under the open circuit voltage of 0.5V is 1.45 omega and 0.147 Omega respectively. N doping can effectively reduce the charge transfer resistance of Li_4Ti_5O_ (12) itself, improve the conductivity of the electrode material itself,.N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotubes are 0.5463 and 0.5135 respectively when the open circuit voltage is 0.5V. Omega, both have lower Warburg impedance, N-Li_4Ti_5O_ (12) nanowires themselves show a teller array structure, and the linear structure also includes mesoporous structure, with a larger specific surface area and higher utilization of active materials; N-Li_4Ti_5O_ (12) nanotube presents a nanotube array structure, and its special structure is not only improved. The specific surface area of the electrode material itself and the effective channel for electron transfer are provided, which improves the utilization rate of the electrode material, the rate of electron transfer and the diffusion rate of lithium ion; at the same time, N doping effectively reduces the band gap of Li_4Ti_5O_ (12), so that more electrons are transferred inside Li_4Ti_5O_ (12), and the electrical conductivity is stronger. For 10A g~ (-1), N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotube electrodes were tested for 500 cycles. The specific capacitance of N-Li_4Ti_5O_ (12) nanowires and N-Li_4Ti_5O_ (12) nanotubes decreased by 5.1% and 1.6% respectively, indicating that all the two electrode materials had good electrochemical stability.

【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O646

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