鈦酸鋰改性及其儲(chǔ)鋰和儲(chǔ)鈉性能研究
發(fā)布時(shí)間：2018-11-17 14:01
【摘要】：能源短缺和環(huán)境污染是當(dāng)今世界面臨的兩大難題,大力開(kāi)發(fā)可再生能源和發(fā)展新能源汽車(chē)是解決這兩大難題的有效途徑,而高效的能量存儲(chǔ)系統(tǒng)是實(shí)現(xiàn)這兩個(gè)途徑的關(guān)鍵。鋰離子電池因其能量密度高,壽命長(zhǎng),環(huán)境友好的特點(diǎn)成為最受歡迎的能量存儲(chǔ)系統(tǒng)。但隨著鋰離子電池的廣泛應(yīng)用,緊缺的鋰資源勢(shì)必會(huì)限制鋰離子電池的可持續(xù)發(fā)展。地殼中鈉資源豐富,因此與鋰離子電池相近的鈉離子電池也被人們關(guān)注。尖晶石鈦酸鋰(Li_4Ti_5O_(12),LTO)是目前安全性能極高,循環(huán)壽命超長(zhǎng)的鋰離子電池負(fù)極材料,同時(shí)也是性能良好的鈉離子電池負(fù)極材料。但是Li_4Ti_5O_(12)的導(dǎo)電性差,嚴(yán)重影響其倍率容量,因此需要改性才能滿足要求。本論文首先評(píng)估了不同方式改性的鈦酸鋰材料的結(jié)構(gòu)特征和電化學(xué)特征,探究結(jié)構(gòu)與性能之間的內(nèi)在關(guān)系,然后研究簡(jiǎn)單高效的改性方法制備高性能的鈦酸鋰負(fù)極材料。主要研究結(jié)果如下:1、通過(guò)對(duì)六種改性鈦酸鋰的綜合評(píng)測(cè),系統(tǒng)研究了體相摻雜,表面改性和減小顆粒尺寸改性的鈦酸鋰的結(jié)構(gòu)特征和儲(chǔ)鋰儲(chǔ)鈉的電化學(xué)特征。結(jié)果表明,無(wú)定形碳和碳納米管包覆的鈦酸鋰具有優(yōu)異的儲(chǔ)鋰性能,而納米化鈦酸鋰材料具有更好的儲(chǔ)鈉性能。2、通過(guò)溶膠-凝膠法制備了Cr改性的鈦酸鋰材料,同時(shí)獲得體相摻雜,表面包覆和尺寸減小的改性效果。結(jié)果表明,Cr~(3+)在體相摻雜使部分的Ti4+轉(zhuǎn)變成Ti~(3+),提高LTO的體相電子電導(dǎo);Li_2CrO4在顆粒表面原位形成,提高電極材料的表面導(dǎo)電性;Li_2CrO4包覆和Cr摻雜共同抑制了LTO顆粒的長(zhǎng)大,獲得小的顆粒尺寸。這種協(xié)同改性效果使Li3.9Cr0.3Ti4.8O12具有優(yōu)異的電化學(xué)性能,其在10C時(shí)的容量達(dá)到141 mAh g-1,1C循環(huán)1000次后還有155 mAh g-1。3、采用液相法制備了Cr_2O_3改性的Li_4Ti_5O_(12)負(fù)極材料。結(jié)果表明:采用堿性鉻溶液能夠獲得純的Cr_2O_3包覆的Li_4Ti_5O_(12)負(fù)極材料;Cr_2O_3能夠增強(qiáng)Li_4Ti_5O_(12)顆粒間的連接,提供更多的電子傳導(dǎo)通道,減小顆粒間的阻抗。此外,Cr_2O_3與Li形成的不可逆相Lix Cr_2O_3能夠使Li7 Ti5O12穩(wěn)定在Li_4Ti_5O_(12)顆粒表面。其中1%Cr_2O_3包覆的Li_4Ti_5O_(12)表現(xiàn)優(yōu)異的倍率性能和低溫性能,在10 C的容量為134 mAh g-1,在-20o C的容量為118 mAh g-1。4、采用聚醚類(lèi)表面活性劑P123輔助水熱法合成超薄的Li_4Ti_5O_(12)納米片并研究了其儲(chǔ)鈉性能。結(jié)果表明:P123能夠抑制Li_2TiO_3的長(zhǎng)大,并且促進(jìn)(Li1.81H0.91)Ti2O5?2H2O前驅(qū)體形成有序結(jié)構(gòu)的納米片。此外,P123還能抑制LTO納米片的堆垛,使得納米片的厚度為4 nm。這種超薄有序的LTO納米片具有優(yōu)異的儲(chǔ)鈉性能,在10 C的可逆容量達(dá)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).
【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：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).
【學(xué)位授予單位】：合肥工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TM912
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