钛酸锂改性及其储锂和储钠性能研究
发布时间：2018-11-17 14:01
【摘要】：能源短缺和环境污染是当今世界面临的两大难题,大力开发可再生能源和发展新能源汽车是解决这两大难题的有效途径,而高效的能量存储系统是实现这两个途径的关键。锂离子电池因其能量密度高,寿命长,环境友好的特点成为最受欢迎的能量存储系统。但随着锂离子电池的广泛应用,紧缺的锂资源势必会限制锂离子电池的可持续发展。地壳中钠资源丰富,因此与锂离子电池相近的钠离子电池也被人们关注。尖晶石钛酸锂(Li_4Ti_5O_(12),LTO)是目前安全性能极高,循环寿命超长的锂离子电池负极材料,同时也是性能良好的钠离子电池负极材料。但是Li_4Ti_5O_(12)的导电性差,严重影响其倍率容量,因此需要改性才能满足要求。本论文首先评估了不同方式改性的钛酸锂材料的结构特征和电化学特征,探究结构与性能之间的内在关系,然后研究简单高效的改性方法制备高性能的钛酸锂负极材料。主要研究结果如下:1、通过对六种改性钛酸锂的综合评测,系统研究了体相掺杂,表面改性和减小颗粒尺寸改性的钛酸锂的结构特征和储锂储钠的电化学特征。结果表明,无定形碳和碳纳米管包覆的钛酸锂具有优异的储锂性能,而纳米化钛酸锂材料具有更好的储钠性能。2、通过溶胶-凝胶法制备了Cr改性的钛酸锂材料,同时获得体相掺杂,表面包覆和尺寸减小的改性效果。结果表明,Cr~(3+)在体相掺杂使部分的Ti4+转变成Ti~(3+),提高LTO的体相电子电导;Li_2CrO4在颗粒表面原位形成,提高电极材料的表面导电性;Li_2CrO4包覆和Cr掺杂共同抑制了LTO颗粒的长大,获得小的颗粒尺寸。这种协同改性效果使Li3.9Cr0.3Ti4.8O12具有优异的电化学性能,其在10C时的容量达到141 mAh g-1,1C循环1000次后还有155 mAh g-1。3、采用液相法制备了Cr_2O_3改性的Li_4Ti_5O_(12)负极材料。结果表明:采用碱性铬溶液能够获得纯的Cr_2O_3包覆的Li_4Ti_5O_(12)负极材料;Cr_2O_3能够增强Li_4Ti_5O_(12)颗粒间的连接,提供更多的电子传导通道,减小颗粒间的阻抗。此外,Cr_2O_3与Li形成的不可逆相Lix Cr_2O_3能够使Li7 Ti5O12稳定在Li_4Ti_5O_(12)颗粒表面。其中1%Cr_2O_3包覆的Li_4Ti_5O_(12)表现优异的倍率性能和低温性能,在10 C的容量为134 mAh g-1,在-20o C的容量为118 mAh g-1。4、采用聚醚类表面活性剂P123辅助水热法合成超薄的Li_4Ti_5O_(12)纳米片并研究了其储钠性能。结果表明:P123能够抑制Li_2TiO_3的长大,并且促进(Li1.81H0.91)Ti2O5?2H2O前驱体形成有序结构的纳米片。此外,P123还能抑制LTO纳米片的堆垛,使得纳米片的厚度为4 nm。这种超薄有序的LTO纳米片具有优异的储钠性能,在10 C的可逆容量达到115 mAh g-1。
[Abstract]:Energy shortage and environmental pollution are two major problems facing the world today. Developing renewable energy and developing new energy vehicles are the effective ways to solve these two problems, and efficient energy storage system is the key to realize these two approaches. Lithium ion battery is the most popular energy storage system because of its high energy density, long life and friendly environment. However, with the wide application of lithium ion batteries, the shortage of lithium resources will limit the sustainable development of lithium ion batteries. The earth's crust is rich in sodium, so sodium ion batteries, which are close to lithium ion batteries, are also concerned. Spinel lithium titanate (Li_4Ti_5O_) (12), LTO) is a kind of anode material for lithium ion battery with high safety and long cycle life. It is also a good anode material for sodium ion battery. However, the conductivity of Li_4Ti_5O_ (12) is poor, which seriously affects the capacity of Li_4Ti_5O_ (12), so it needs to be modified to meet the requirements. In this paper, the structure and electrochemical characteristics of lithium titanate modified in different ways were evaluated, and the relationship between structure and properties was explored. Then, the preparation of high performance lithium titanate anode material by simple and efficient modification method was studied. The main results are as follows: 1. Through the comprehensive evaluation of six kinds of modified lithium titanate, the structure characteristics and electrochemical characteristics of lithium titanate doped, surface modified and reduced particle size modified lithium titanate were systematically studied. The results showed that amorphous carbon and carbon nanotube coated lithium titanate had excellent lithium storage performance, while nanometer lithium titanate material had better sodium storage performance. 2. Cr modified lithium titanate material was prepared by sol-gel method. At the same time, the modification effects of bulk doping, surface coating and size reduction were obtained. The results showed that Cr~ (3) doped in bulk changed part of Ti4 into Ti~ (3), which enhanced the bulk electronic conductivity of LTO, and Li_2CrO4 formed in situ on the surface of particles to improve the surface conductivity of electrode materials. Li_2CrO4 coating and Cr doping inhibit the growth of LTO particles and obtain small particle size. The synergistic modification results in the excellent electrochemical properties of Li3.9Cr0.3Ti4.8O12. The capacity of Li3.9Cr0.3Ti4.8O12 reaches 141 mAh g-1C at 10 C and 155 mAh g-1.3 after 1000 cycles. Cr_2O_3 modified Li_4Ti_5O_ (12) anode materials were prepared by liquid phase method. The results show that the pure Cr_2O_3 coated Li_4Ti_5O_ (12) anode material can be obtained by alkaline chromium solution. Cr_2O_3 can enhance the connection between Li_4Ti_5O_ (12) particles, provide more electron conduction channels, and reduce the impedance between particles. In addition, the irreversible phase Lix Cr_2O_3 formed by Cr_2O_3 and Li can stabilize Li7 Ti5O12 on the surface of Li_4Ti_5O_ (12) particles. The Li_4Ti_5O_ (12) coated with 1%Cr_2O_3 exhibited excellent performance at low temperature and rate, with a capacity of 134 mAh g-1 at 10 C and 118 mAh g-1.4 at -20 o C. Ultrathin Li_4Ti_5O_ (12) nanoparticles were synthesized by P123-assisted hydrothermal method with polyether surfactants and their sodium storage properties were studied. The results show that P123 can inhibit the growth of Li_2TiO_3 and promote the formation of (Li1.81H0.91) Ti2O5?2H2O precursors with ordered structure. In addition, P123 can also inhibit the stacking of LTO nanocrystals, so that the thickness of the nanoparticles is 4 nm.. The ultrathin and ordered LTO nanocrystals have excellent sodium storage properties, and the reversible capacity at 10 C reaches 115 mAh g ~ (-1).
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
[Abstract]:Energy shortage and environmental pollution are two major problems facing the world today. Developing renewable energy and developing new energy vehicles are the effective ways to solve these two problems, and efficient energy storage system is the key to realize these two approaches. Lithium ion battery is the most popular energy storage system because of its high energy density, long life and friendly environment. However, with the wide application of lithium ion batteries, the shortage of lithium resources will limit the sustainable development of lithium ion batteries. The earth's crust is rich in sodium, so sodium ion batteries, which are close to lithium ion batteries, are also concerned. Spinel lithium titanate (Li_4Ti_5O_) (12), LTO) is a kind of anode material for lithium ion battery with high safety and long cycle life. It is also a good anode material for sodium ion battery. However, the conductivity of Li_4Ti_5O_ (12) is poor, which seriously affects the capacity of Li_4Ti_5O_ (12), so it needs to be modified to meet the requirements. In this paper, the structure and electrochemical characteristics of lithium titanate modified in different ways were evaluated, and the relationship between structure and properties was explored. Then, the preparation of high performance lithium titanate anode material by simple and efficient modification method was studied. The main results are as follows: 1. Through the comprehensive evaluation of six kinds of modified lithium titanate, the structure characteristics and electrochemical characteristics of lithium titanate doped, surface modified and reduced particle size modified lithium titanate were systematically studied. The results showed that amorphous carbon and carbon nanotube coated lithium titanate had excellent lithium storage performance, while nanometer lithium titanate material had better sodium storage performance. 2. Cr modified lithium titanate material was prepared by sol-gel method. At the same time, the modification effects of bulk doping, surface coating and size reduction were obtained. The results showed that Cr~ (3) doped in bulk changed part of Ti4 into Ti~ (3), which enhanced the bulk electronic conductivity of LTO, and Li_2CrO4 formed in situ on the surface of particles to improve the surface conductivity of electrode materials. Li_2CrO4 coating and Cr doping inhibit the growth of LTO particles and obtain small particle size. The synergistic modification results in the excellent electrochemical properties of Li3.9Cr0.3Ti4.8O12. The capacity of Li3.9Cr0.3Ti4.8O12 reaches 141 mAh g-1C at 10 C and 155 mAh g-1.3 after 1000 cycles. Cr_2O_3 modified Li_4Ti_5O_ (12) anode materials were prepared by liquid phase method. The results show that the pure Cr_2O_3 coated Li_4Ti_5O_ (12) anode material can be obtained by alkaline chromium solution. Cr_2O_3 can enhance the connection between Li_4Ti_5O_ (12) particles, provide more electron conduction channels, and reduce the impedance between particles. In addition, the irreversible phase Lix Cr_2O_3 formed by Cr_2O_3 and Li can stabilize Li7 Ti5O12 on the surface of Li_4Ti_5O_ (12) particles. The Li_4Ti_5O_ (12) coated with 1%Cr_2O_3 exhibited excellent performance at low temperature and rate, with a capacity of 134 mAh g-1 at 10 C and 118 mAh g-1.4 at -20 o C. Ultrathin Li_4Ti_5O_ (12) nanoparticles were synthesized by P123-assisted hydrothermal method with polyether surfactants and their sodium storage properties were studied. The results show that P123 can inhibit the growth of Li_2TiO_3 and promote the formation of (Li1.81H0.91) Ti2O5?2H2O precursors with ordered structure. In addition, P123 can also inhibit the stacking of LTO nanocrystals, so that the thickness of the nanoparticles is 4 nm.. The ultrathin and ordered LTO nanocrystals have excellent sodium storage properties, and the reversible capacity at 10 C reaches 115 mAh g ~ (-1).
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
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