本文選題：磷酸鐵鋰 + 溶膠-凝膠��； 參考：《武漢工程大學(xué)》2015年碩士論文

【摘要】：LiFePO_4正極材料因其特有的橄欖石晶體結(jié)構(gòu)而具備了能使鋰離子嵌入和脫出的充放電能力,這是它能成為正極材料的理論基礎(chǔ),其原材料易得且價(jià)格便宜、有較高的工作電壓、安全無(wú)毒、理論比容量大、綠色環(huán)保且熱穩(wěn)定性好,是已初步商業(yè)化應(yīng)用和具有理想前景的鋰離子電池正極材料。但是,同樣因?yàn)長(zhǎng)iFePO_4自身的結(jié)構(gòu)和組成的特點(diǎn)而使其本身電子電導(dǎo)率很低,且鋰離子在晶體間擴(kuò)散能力差。這些都限制了它的應(yīng)用前景,有很多方法可以提高LiFePO_4正極材料電化學(xué)性能,其中摻雜改性是的最常用且有效的途徑。在本文中,首先綜述了LiFePO_4正極材料的發(fā)展和主要研究方向以及石墨烯作為導(dǎo)電材料的應(yīng)用等。具體研究了石墨烯摻雜改性L(fǎng)iFePO_4正極材料的摻雜量和不同摻雜階段對(duì)其電化學(xué)性能的影響,在最優(yōu)化的摻雜量和摻雜階段下同時(shí)加入鎂離子的影響等,并挑選了幾種稀土金屬元素中較便宜的金屬離子進(jìn)行摻雜的探索性實(shí)驗(yàn)。以進(jìn)一步優(yōu)化LiFePO_4的電容量、循環(huán)與倍率性能等,促進(jìn)鋰離子電池的商業(yè)化發(fā)展,也為L(zhǎng)iFePO_4正極材料以及其他正積極材料的摻雜改性提供新的思路。主要研究結(jié)果和內(nèi)容如下:采用溶膠-凝膠法合成了碳包覆的LiFePO_4/C正極材料,并在其前驅(qū)體合成階段分別加入了四種不同量的鑭系稀土金屬元素:氧化銩(Tm2O3)、氧化釤(Sm2O3)、氧化鈰(CeO2)、氧化釓(Gd2O3),對(duì)LiFePO_4/C分別進(jìn)行了質(zhì)量百分比分別為1%、2%、3%、5%的摻雜實(shí)驗(yàn),其中摻雜1%Gd3+、1%Ce4+和2%Ce4+會(huì)使LiFePO_4/C的電化學(xué)性能提高,而摻雜1%Gd3+的效果最好,在0.1C下LiFePO_4/C的比容量可達(dá)135.7mAh/g,10C下為85.5mAh/g,其50次充放電循環(huán)后任可保持93.3%的比容量,并具有較好的晶體結(jié)構(gòu)和微觀形貌。此外還在其不同合成的階段分別加入了不同質(zhì)量的石墨烯,通過(guò)XRD、SEM、Raman、振實(shí)密度儀和電池測(cè)試系統(tǒng)等對(duì)所制備的LiFePO_4/C的結(jié)構(gòu)、形貌、組成以及各種電化學(xué)性能進(jìn)行了測(cè)試,結(jié)果表明:LiFePO_4/C正極材料的比電容量隨著石墨烯摻雜量的增加而增加,且在二次球磨前加入石墨烯的效果最好,但從經(jīng)濟(jì)實(shí)用、石墨烯的使用效率、振實(shí)密度這三個(gè)角度出發(fā),2%石墨烯摻雜量的效果最好,其首次放電比容量為151.3mAh/g(0.1C),在10C下為122.4mAh/g,在0.1C下50次充放電循環(huán)后其比容量只損失了2.13%,它的振實(shí)密度為1.17 g/cm3,單位體積容量為177.0 mAh/cm3。然而在二次球磨前加入5%石墨烯的LiFePO_4/C正極材料其首次放電比容量為159.6 mAh/g,但在0.1C下50次充放電循環(huán)后,其比容量損失了6.23%,且單位體積容量?jī)H為150.0mAh/cm3�；趯�(duì)LiFePO_4/C正極材料摻雜改性的優(yōu)化機(jī)理不同,在最優(yōu)化的條件下同時(shí)摻雜了已知對(duì)其電化學(xué)性能有較好改善的鎂離子,在摻雜2%鎂離子時(shí),在0.1C下首次放電比容量為162.7mAh/g(理論容量的95.7%),循環(huán)50次后其比容量損失了6.23%,其單位體積容量高達(dá)195.2mAh/cm3。
[Abstract]:Due to its unique olivine crystal structure, LiFePO_4 cathode materials have the ability to charge and discharge lithium ions embedded and removed. This is the theoretical basis for LiFePO_4 cathode materials. The raw materials are easy to obtain, the price is low, and the working voltage is high. It is a promising cathode material for lithium-ion batteries, which is safe and non-toxic, has large theoretical capacity, is environmentally friendly and has good thermal stability. However, due to the structure and composition of LiFePO_4 itself, the electronic conductivity of LiFePO_4 is very low, and the diffusion ability of lithium ion between crystals is poor. There are many ways to improve the electrochemical performance of LiFePO_4 cathode materials, among which doping modification is the most common and effective way. In this paper, the development and research direction of LiFePO_4 cathode materials and the application of graphene as conductive materials are reviewed. The influences of the doping amount of graphene doped LiFePO_4 cathode materials and the different doping stages on their electrochemical properties were studied in detail, and the effect of the addition of magnesium ions at the optimal doping level and the doping stage was also studied. Some cheaper metal ions of rare earth elements were selected for the exploratory experiment. In order to further optimize the capacity, cycle and rate performance of LiFePO_4, the commercial development of lithium-ion batteries is promoted, and a new idea for doping modification of LiFePO_4 cathode materials and other positive materials is also provided. The main results and contents are as follows: carbon coated LiFePO_4/C cathode materials were synthesized by sol-gel method. Four different amounts of lanthanide rare earth elements were added in the precursor synthesis stage: thulium Tm2O3 oxide, samarium oxide Sm2O3O _ 3, cerium oxide CeO2O _ 2, gadolinium oxide Gd _ 2O _ 3O _ 3O _ 3O _ 3, respectively. The LiFePO_4/C was doped with a mass percentage of 1 ~ (2 +) ~ (35)%, respectively. The electrochemical performance of LiFePO_4/C was improved by doping 1%Gd3, 14 and 24, but the effect of doped 1%Gd3 was the best. The specific capacity of LiFePO_4/C at 0.1C was up to 85.5 mg / g at 135.7 mAh/ g / g 10C, and the specific capacity of LiFePO_4/C could be maintained at 93.3% after 50 cycles of charge and discharge. It has good crystal structure and microstructure. In addition, graphene of different quality was added in different synthesis stages. The structure, morphology, composition and electrochemical properties of LiFePO_4/C were tested by XRDX SEMN Raman, vibrator density meter and battery test system. The results show that the specific capacitance increases with the increase of graphene doping, and the effect of adding graphene before secondary ball milling is the best. However, it is economical and practical to use graphene. The effect of 2% graphene doping is the best from the three angles of vibrational density. Its initial discharge capacity is 151.3 mAh/ g ~ (-1) C ~ (-1), and it is 122.4 m / g at 10C. After 50 charge-discharge cycles at 0.1 C, the specific capacity is only 2.13%. Its vibrational density is 1.17 g / cm ~ (-3), and the unit volume capacity is 177.0 mAh路 cm ~ (3). However, the first discharge specific capacity of the LiFePO_4/C cathode material added 5% graphene before secondary ball milling is 159.6 mAh/ g, but after 50 charge-discharge cycles at 0.1C, the specific capacity is 6.23 and the unit volume capacity is only 150.0mAh/ cm ~ (-3). Based on the different mechanism of doping modification of LiFePO_4/C cathode materials, magnesium ions, which are known to improve the electrochemical performance of LiFePO_4/C cathode materials, have been doped at the same time under the optimized conditions, and when 2% magnesium ions are doped, The first discharge capacity at 0.1C is 162.7mAh / g (the theoretical capacity is 95.7g). After 50 cycles, the specific capacity is 6.23g, and its unit volume capacity is up to 195.2mAh路 cm ~ (-3).
【學(xué)位授予單位】：武漢工程大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：TQ131.11;TM912

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