本文選題：生物仿生合成 + 纖維素��； 參考：《浙江大學》2017年博士論文

【摘要】：近年來,隨著納米科技的進步,鋰離子電池的性能有了很大的提高,但是仍然存在許多瓶頸,尤其是在新型高性能電極材料的設計及構(gòu)筑方面還面臨挑戰(zhàn)。作為未來鋰離子電池理想的負極材料,硅基材料由于具有遠高于傳統(tǒng)商用石墨負極的理論比容量,受到極大的關注。但是如何解決硅基負極材料較低的導電性和在鋰離子嵌入和脫出過程中巨大的體積變化是進一步提高其電化學性能的關鍵。基于自組裝的仿生合成技術,它將客體基質(zhì)的化學性能和生物物質(zhì)優(yōu)異的結(jié)構(gòu)功能特點相結(jié)合,為設計和制備具有特定結(jié)構(gòu)和性能的新的功能材料提供了一個有效途徑。自然纖維素物質(zhì)作為一種常見的天然高分子化合物,具有從宏觀到分子層次的獨特階層結(jié)構(gòu)及其在納米層級上的多孔網(wǎng)狀形貌,以其為模板或支架在構(gòu)筑納米結(jié)構(gòu)電極材料中有很大的應用潛力。本論文的主要研究內(nèi)容是以自然纖維素物質(zhì)(實驗室常用的定量濾紙)為模板和支架,實現(xiàn)了多種納米纖維結(jié)構(gòu)的硅基復合材料的制備,并較好的緩解了硅基負極材料在充放電過程中體積變化所導致的材料結(jié)構(gòu)破壞,增強了其機械性能和導電性,改善了其電化學儲能性能,為其在儲能器件中的應用提供一定的指導。主要研究內(nèi)容如下:1.以自然纖維素物質(zhì)(實驗室普通定量濾紙)為模板和碳支架,采用簡單的溶膠-凝膠法將二氧化硅凝膠層組裝到濾紙纖維素纖維的表面,經(jīng)碳化得到納米纖維結(jié)構(gòu)的二氧化硅/碳復合材料。該復合材料中,納米級厚度的二氧化硅層均勻的包覆在碳纖維的表面。由于該復合材料具有多孔網(wǎng)狀結(jié)構(gòu)、高比表面積以及碳納米纖維基底,有利于電解液擴散和提高二氧化硅的導電性,有效緩沖了二氧化硅在充放電過程中巨大的體積變化,因此在用作鋰離子電池負極材料時,表現(xiàn)出較高的比容量,較好的循環(huán)穩(wěn)定性和倍率性能。進一步包覆無定形碳層或者沉積銀納米顆粒于二氧化硅/碳納米纖維的表面,其電化學性能得到了進一步提高。2.為了進一步提高二氧化硅/碳復合材料的電化學性能,采用鎂熱還原法,將復合材料中二氧化硅還原為硅,得到了納米纖維結(jié)構(gòu)的硅/碳復合材料。該復合材料完整地保留了濾紙原有的多孔網(wǎng)狀結(jié)構(gòu),納米級厚度的硅層均勻的包覆在碳纖維的表面。當用作鋰離子電池負極材料時,硅含量為25.7wt%,硅層厚度為40nm時,該復合材料的電化學性能最好。在100 mA g-1電流密度下,循環(huán)150次以后,放電比容量還可以保持在750.6 mAh g-1。將無定形碳層或者銀納米顆粒沉積在硅/碳納米纖維表面,其電化學性能得到了進一步提高,在100mAg-1電流密度下,循環(huán)150次以后,放電比容量分別為775.3和1018.7 mAhg-1。3.以自然纖維素物質(zhì)(濾紙)為模板,首先將二氧化硅凝膠膜包覆在濾紙納米纖維表面,再用表面凝膠-溶膠法均勻的包覆一定厚度的二氧化鈦凝膠層,經(jīng)后續(xù)的煅燒和鎂熱還原處理,制備了納米纖維結(jié)構(gòu)的二氧化鈦/硅復合材料。該復合材料中,銳鈦礦型二氧化鈦納米顆粒層均勻完整的包覆在硅納米纖維表面。當用作鋰離子電池負極材料時,二氧化鈦含量為54.3 wt%時,復合材料的電化學性能最好。在200 mA g-1電流密度下,循環(huán)200次以后,放電比容量為498.9 mAh g-1。由于復合材料的多孔網(wǎng)狀結(jié)構(gòu)以及二氧化鈦層的均勻完整的包覆,有利于緩沖硅充放電過程中產(chǎn)生的巨大體積變化,增強電極材料的結(jié)構(gòu)穩(wěn)定性。因此制備的二氧化鈦/硅納米復合材料表現(xiàn)出增強的循環(huán)穩(wěn)定性和倍率性能。4.以自然纖維素物質(zhì)(濾紙)為模板和碳支架,結(jié)合自組裝和低溫鎂熱還原方法,制備了納米纖維結(jié)構(gòu)的TiOx/carbon/silicon復合材料。該材料在微觀上具有獨特的多孔網(wǎng)狀結(jié)構(gòu)及形貌特征,硅薄層(厚度～50 nm)夾在多孔碳納米纖維和外面具有氧缺陷的二氧化鈦薄層之間,并且二氧化鈦層由大小約為5 nm的銳鈦礦型二氧化鈦納米顆粒堆積而成,二氧化鈦顆粒表面覆蓋一層超薄無定形的碳層。將該復合材料應用于鋰離子電池負極材料,由于多孔網(wǎng)狀的碳支架、外層具有氧缺陷二氧化鈦薄層、硅薄層的協(xié)同作用,該復合材料表現(xiàn)出較高的比容量和很好的倍率性能。當二氧化鈦含量為24.1 wt%時,該復合材料在100mAg-1電流密度下,循環(huán)160次以后,放電比容量為792.6mAhg-1。相比沒有鈦氧化物層包裹的納米纖維結(jié)構(gòu)的硅/碳復合材料,該納米復合材料的比容量和循環(huán)穩(wěn)定性得到了很大的提高。5.以天然纖維素物質(zhì)(濾紙)為模板,制備了納米纖維結(jié)構(gòu)的二氧化錫/硅復合材料。該復合材料中,二氧化錫納米顆粒均勻的分散在硅納米纖維表面。首先以濾紙為模板采用鎂熱還原法制備了硅納米纖維材料,然后通過溶膠-凝膠方法在硅納米纖維表面沉積二氧化錫凝膠層,再在惰性氣中經(jīng)過煅燒得到了二氧化錫/硅納米復合材料。該復合材料具有原始濾紙模板的多孔網(wǎng)狀結(jié)構(gòu),當用作鋰離子電池負極材料時,比單一的二氧化錫納米顆粒和硅納米纖維材料表現(xiàn)出更好的電化學性能。當二氧化錫含量為58.8wt%時,該納米復合材料在100mAg-1電流密度下,150次充放電循環(huán)以后,可逆比容量為54S.8mAhg-1。增強的電化學性能主要是因為復合材料的多孔網(wǎng)狀結(jié)構(gòu),二氧化錫納米顆粒的均勻分散以及二氧化錫和硅之間的協(xié)同作用。硅基材料,尤其是具有特殊結(jié)構(gòu)的硅基復合材料,一直是鋰離子電池負極材料研究的重點。本論文制備了一系列基于天然纖維素物質(zhì)的納米纖維結(jié)構(gòu)的硅基復合材料,并對其電化學性能進行了研究。得益于自然纖維素物質(zhì)高比表面和多孔網(wǎng)狀結(jié)構(gòu),使得有關活性負極材料在充放電過程中體積變化所導致的材料結(jié)構(gòu)破壞得到了緩解,增強了其機械性能和導電性,達到了更好的電池穩(wěn)定性、較高的能量密度和較優(yōu)的循環(huán)性能,從而提高了硅基負極材料的電化學性能。本論文工作表明基于自組裝的仿生合成方法在設計制備高性能能源相關的電極材料方面具有很大的應用前景。
[Abstract]:In recent years, with the progress of nanotechnology, the performance of lithium ion batteries has been greatly improved, but there are still many bottlenecks, especially in the design and construction of new high performance electrode materials. As the ideal anode material for lithium ion batteries in the future, silicon based materials are far higher than the traditional commercial graphite negative. But how to solve the low conductivity of silicon based negative electrode and the huge volume change in the process of inserting and releasing lithium ion is the key to further improve its electrochemical performance. The combination of structural and functional characteristics provides an effective way for the design and preparation of new functional materials with specific structures and properties. As a common natural polymer compound, natural cellulose material has a unique hierarchical structure from macro to molecular levels and its porous network morphology at the nanoscale level. The main research content of this paper is the preparation of a variety of nanofiber structure silicon based composites by using natural cellulose material (the commonly used quantitative filter paper in the laboratory) as the template and scaffold, and it is better to alleviate the charge and discharge of the silicon negative electrode materials. The material structure damage caused by the volume change in the process has enhanced its mechanical properties and electrical conductivity, improved its electrochemical energy storage performance, and provided some guidance for its application in energy storage devices. The main contents are as follows: 1. using natural cellulose material (laboratory fixed filter paper) as a template and carbon scaffold, simple sols are used. The silica gel layer is assembled on the surface of the filter paper cellulose fiber, and the silica / carbon composites of nanofiber structure are obtained by carbonization. In this composite, the nanometer thickness silica layer is coated evenly on the surface of carbon fiber. The composite has a porous network structure, high specific surface area and carbon. The nano fiber substrate is beneficial to the diffusion of electrolyte and the increase of the conductivity of silicon dioxide, which effectively cushions the huge volume change of silicon dioxide during the charge and discharge process. Therefore, when used as a anode material for lithium ion batteries, it shows higher specific capacity, better cycling stability and multiple performance. The electrochemical properties of the deposited silver nanoparticles on the surface of silica / carbon nanofibers have been further improved by.2. in order to further improve the electrochemical performance of silica / carbon composites. The reduction of silica in the composite materials to silicon by magnesium thermal reduction is used. The composite material of nanofiber structure is obtained. The material has retained the original porous network structure of the filter paper, and the nanoscale silicon layer is coated evenly on the surface of carbon fiber. When used as a lithium ion battery negative material, the silicon content is 25.7wt% and the thickness of the silicon layer is 40nm, the electrochemical performance of the composite is best. The discharge ratio is 150 times after the cycle of 100 mA g-1 density. The capacity can also be kept at 750.6 mAh g-1. by depositing amorphous carbon or silver nanoparticles on the surface of silicon / carbon nanofibers. The electrochemical performance is further improved. Under the current density of 100mAg-1, the discharge specific capacity is 775.3 and 1018.7 mAhg-1.3., respectively, after 150 cycles, first of the natural cellulose material (filter paper) as a template. The silica gel membrane was coated on the surface of the filter paper nanofibers, then the titanium dioxide gel layer with a certain thickness was coated evenly with the surface gel sol method. The nanofiber structure titanium dioxide / silicon composite was prepared by subsequent calcining and magnesium heat reduction. When used as a anode material for lithium ion batteries, when used as a anode material for lithium ion batteries, the electrochemical performance of the composite is the best when the content of titanium dioxide is 54.3 wt%. Under the 200 mA g-1 current density, the discharge specific capacity is 498.9 mAh g-1. due to the porous network structure of the composite and the titanium dioxide layer. A uniform coating is beneficial to the huge volume change produced during the charging and discharging of the buffer silicon, and the structural stability of the electrode material is enhanced. Therefore, the prepared titanium dioxide / silicon nanocomposites exhibit enhanced cyclic stability and multiplying performance.4. with natural cellulose material (filter paper) as a template and carbon scaffold, combined with self-assembly and low temperature. The TiOx/carbon/silicon composite of nanofiber structure has been prepared by the method of magnesium reduction. The material has unique porous network structure and morphologies on the microcosmic. The silicon thin layer (thickness to 50 nm) is sandwiched between the porous carbon nanofibers and the thin layer of oxygen deficient titanium dioxide, and the TiO2 layer is about 5 nm in size. Anatase titanium dioxide nanoparticles are stacked, and the surface of titanium dioxide particles is covered with a layer of ultra-thin amorphous carbon layer. The composite material is applied to the anode material of lithium ion battery. Due to the porous network of carbon scaffold, the outer layer has the thin layer of oxygen defect titanium dioxide and the synergistic action of silicon thin layer, the composite shows a higher ratio. When the content of titanium dioxide is 24.1 wt%, the composite material has no silicon / carbon composites with nanofiber structure wrapped in titanium oxide layer at 100mAg-1 current density and after 160 cycles at the current density, and the specific capacity and cyclic stability of the nanocomposite have been obtained. The two tin / silicon composite material with nanofiber structure was prepared by using the natural cellulose material (filter paper) as a template. In this composite, the two tin nanoparticles were evenly dispersed on the surface of silicon nanofibers. First, the silicon nanofibers were prepared by the magnesium heat reduction method with the filter paper as the template, and then the sol-gel was prepared by the sol-gel process. The gel method deposited two tin oxide gel layer on the surface of silicon nanofibers, and then calcined in the inert gas to get two tin / silicon nanocomposites. The composite has a porous network structure of the original filter paper template. When used as the anode material for lithium ion batteries, it is better than the single two tin oxide nanoparticles and silicon nanofiber material. When the content of two tin oxide is 58.8wt%, the electrochemical performance of the nanocomposite at the current density of 100mAg-1 and the 150 charge discharge cycle, the reversible specific capacity of 54S.8mAhg-1. is mainly due to the porous network structure of the composite, the uniform dispersion of two tin oxide nanoparticles and two oxidation. The synergistic effect between tin and silicon. Silicon-based materials, especially silicon based composites with special structures, have always been the focus of research on anode materials for lithium ion batteries. A series of silicon based composites based on nanofiber structures based on natural cellulose materials have been prepared in this paper, and their electrochemical properties are studied. The high specific surface and porous network structure of cellulose make the destruction of material structure caused by the volume change of the active anode material in the process of charge discharge and discharge, enhance its mechanical properties and electrical conductivity, achieve better battery stability, higher energy density and better cycling performance, thus increasing the negative silicon base. The electrochemical performance of polar materials shows that the bionic synthesis method based on self-assembly has great potential in the design and preparation of high performance energy related electrode materials.
【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TB332;TM912

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本文編號：1953289