發(fā)布時(shí)間：2018-05-10 16:47

  本文選題：鋰離子電池 + 磷酸鐵鋰��； 參考：《天津大學(xué)》2014年博士論文

【摘要】：鋰離子電池由于具有快速充放，無(wú)記憶效應(yīng)以及高容量等優(yōu)勢(shì)，已經(jīng)成為新能源發(fā)展主要的方向。磷酸鐵鋰作為鋰離子電池正極材料，由于原料來(lái)源廣泛，對(duì)環(huán)境友好，使用安全等諸多優(yōu)點(diǎn)逐漸成為動(dòng)力型鋰離子電池的主要材料。但是磷酸鐵鋰因?yàn)樽陨磔^低的電導(dǎo)率與能量密度限制了其在鋰離子電池中的大規(guī)模應(yīng)用，因此對(duì)磷酸鐵鋰進(jìn)行改性使其具有優(yōu)秀的倍率性能與循環(huán)性能成為本文研究的主要內(nèi)容。本文主要的研究?jī)?nèi)容包括石墨烯(GS)與磷酸鐵鋰的制備，并以碳和石墨烯兩種不同類型的碳源對(duì)其進(jìn)行改性，優(yōu)化制備出性能優(yōu)越的磷酸鐵鋰/石墨烯復(fù)合正極材料。 在石墨烯的制備過(guò)程中，本文首次采用一種在室溫環(huán)境下，以LiAlH4與PBr3作為雙重還原劑還原氧化石墨來(lái)快速制備石墨烯的方法。結(jié)果表明所制備的石墨烯層數(shù)較少，約為三層左右。作為負(fù)極材料應(yīng)用于鋰半電池，在電流密度為100mA/g下，首次充放電比容量分別為1029.4，855.1mAh/g，庫(kù)倫效率可以達(dá)到83.1%。經(jīng)過(guò)21次循環(huán)后，，可逆放電比容量仍然可以達(dá)到760.7mAh/g，顯示出了優(yōu)秀的循環(huán)穩(wěn)定性能。 在LiFePO4前驅(qū)體的制備過(guò)程中，本文分別采用溶膠-凝膠、溶劑熱兩種方法。研究發(fā)現(xiàn)采用溶劑熱法制備的LiFePO4/C樣品具有非常優(yōu)秀的微觀形貌與電化學(xué)性能，并對(duì)反應(yīng)時(shí)間、反應(yīng)溫度以及碳含量進(jìn)行了詳細(xì)的考察。結(jié)果表明在130℃反應(yīng)5h，葡萄糖加入量為15%時(shí)制備的樣品具有較好的結(jié)晶度與分散性。在0.2，0.5，1，3C倍率下，放電比容量分別為159.4，155.6，151.9，141.9mAh/g，具有非常優(yōu)秀的倍率性能。在5，10，20，30C倍率下循環(huán)100次，容量保持率分別為97.0%，99.6%，97.1%，95.6%，顯示出優(yōu)秀的循環(huán)穩(wěn)定性能。 在LiFePO4/GS復(fù)合電極材料的制備過(guò)程中，主要研究了石墨烯的加入量對(duì)復(fù)合材料形貌與電化學(xué)性能的影響。研究發(fā)現(xiàn)在制備LiFePO4/GS復(fù)合材料過(guò)程中，石墨烯加入量過(guò)少會(huì)導(dǎo)致晶體具有較大顆粒；石墨烯加入量過(guò)多會(huì)在LiFePO4顆粒表面包裹較厚的石墨烯層，導(dǎo)致電化學(xué)性能下降。結(jié)果表明當(dāng)石墨烯加入量為5%時(shí)制備的LiFePO4/GS樣品表現(xiàn)最佳，晶體顆粒大小約為100nm，在LiFePO4表面所包裹的石墨烯層數(shù)約為4~5層。在0.2，0.5，1，5C倍率下，放電比容量分別為154.4，150.5，145.9，124.3mAh/g；在5C倍率下循環(huán)200次容量保持率為99.1%，說(shuō)明復(fù)合材料具有非常好的倍率性能與循環(huán)壽命。
[Abstract]:Li-ion batteries have become the main direction of new energy development due to their advantages of rapid charging, memory free and high capacity. As the cathode material of lithium ion battery, lithium iron phosphate has become the main material of power lithium ion battery because of its wide source, friendly to the environment, safe use and so on. However, lithium iron phosphate has limited its large-scale application in lithium-ion batteries because of its low conductivity and energy density. Therefore, the modification of lithium iron phosphate to make it have excellent rate performance and cycle performance has become the main content of this paper. The main research contents in this paper include the preparation of graphene glutathione (GSH) and lithium ferric phosphate, and the modification of them with two different carbon sources, carbon and graphene, to optimize the preparation of lithium iron phosphate / graphene composite cathode material with superior properties. In the process of preparation of graphene, a method of rapid preparation of graphene by reducing graphite oxide with LiAlH4 and PBr3 at room temperature was used for the first time. The results show that the number of graphene layers is less, about three layers. The first charge / discharge capacity is 1029.4855.1 mg / g at current density of 100mA/g, and the Coulomb efficiency can reach 83.1%. After 21 cycles, the specific capacity of reversible discharge can still reach 760.7 mg / g, showing excellent cyclic stability. In the preparation of LiFePO4 precursors, sol-gel and solvothermal methods were used in this paper. It was found that the LiFePO4/C samples prepared by solvothermal method had excellent micromorphology and electrochemical properties, and the reaction time, reaction temperature and carbon content were investigated in detail. The results show that the samples prepared at 130 鈩

本文編號(hào)：1870087