本文選題：納米電極材料 + 硅酸亞鐵鋰��； 參考：《武漢理工大學(xué)》2014年博士論文

【摘要】：基于化學(xué)能/電能儲存與轉(zhuǎn)化的新型電池及器件是當(dāng)前科學(xué)研究的熱點(diǎn)與重點(diǎn)。鋰離子電池以其質(zhì)量輕體積小、儲存容量高、壽命長、安全性能高和環(huán)境友好等優(yōu)點(diǎn)，在能量儲存和轉(zhuǎn)化領(lǐng)域具有廣闊的應(yīng)用前景。然而，受限于傳統(tǒng)正極材料較低的能量密度和功率密度，鋰離子電池還難以滿足下一代高端的動力電池設(shè)備要求。新型的硅酸鹽正極材料具有理論比容量高，資源豐富，價格便宜，以及安全性能高等特性。其中中Li2FeSiO4由于具有穩(wěn)定的循環(huán)性能，越來越受到人們的青睞，具有廣闊的應(yīng)用前景。然而，Li2FeSiO4正極材料低的電導(dǎo)率和鋰離子擴(kuò)散動力學(xué)，，限制了其應(yīng)用。 本文針對Li2FeSiO4正極材料存在的問題，通過結(jié)構(gòu)設(shè)計與調(diào)控，制備了多維的高比容量、長壽命、高倍率性能的納米Li2FeSiO4鋰離子電池電極材料，主要獲得了以下創(chuàng)新性研究成果： 1.通過水熱法和有機(jī)聚合法制備了零維(0D)Li2FeSiO4納米晶/網(wǎng)絡(luò)碳復(fù)合鋰離子電池正極材料。得益于網(wǎng)絡(luò)碳的優(yōu)異導(dǎo)電性和納米晶的鋰離子快速傳輸，這種新穎的復(fù)合材料在0.1C的倍率下具有1.28個鋰離子脫嵌的比容量，實現(xiàn)了從Fe2+到Fe3+，再到Fe4+的連續(xù)兩部的氧化反應(yīng)。在0.5，1，2，5和10C的不同倍率下，比容量分別達(dá)到189.8，175.6，148.9，125.7和106.6mAh/g；經(jīng)過高倍率回到1C后，其比容量仍然達(dá)到175mAh/g。特別值得指出的是，在10C倍率下經(jīng)1000次循環(huán)后，其比容量仍然高達(dá)90.9mAh/g，保持率為97.7%，具有優(yōu)異的倍率循環(huán)性能。 2.采用一種更廉價的三價鐵源水熱還原制備了一維（1D）Li2FeSiO4納米棒材料。研究發(fā)現(xiàn)，單一的Li2FeSiO4材料由于充放電過程中容易團(tuán)聚，引起比容量的快速衰減。為此，實驗采用了一種簡單的PVP錨定法將納米棒錨定于石墨烯片上，有效地抑制了活性材料的團(tuán)聚。而且，其中的石墨烯還能起到電子傳輸和緩解應(yīng)力作用。制備的納米棒狀Li2FeSiO4/石墨烯片復(fù)合材料具有優(yōu)異的電化學(xué)性能：當(dāng)作為鋰離子電池正極材料在1.5-4.8V之間進(jìn)行充放電時，在0.01A/g（1/16C）的電流密度下的放電比容量為298mAh/g，且具有高的倍率性能和長的循環(huán)壽命；當(dāng)作為鋰離子電池負(fù)極材料在0-3V之間進(jìn)行充放電時，在0.02A/g（2/16C）的電流密度下的首次放電比容量為1530mAh/g，隨后的可逆容量為1160mAh/g，倍率性能和循環(huán)穩(wěn)定性能也非常突出。因此，采用石墨烯修飾納米棒狀Li2FeSiO4復(fù)合電極材料具有優(yōu)異的電化學(xué)性能，完全適合下一代動力鋰離子電池的需要。 3.通過乙二醇輔助的一步水熱法制備了具有等級梭形結(jié)構(gòu)的Li2FeSiO4材料。研究發(fā)現(xiàn)，梭形結(jié)構(gòu)是由單晶的納米片構(gòu)筑而成。經(jīng)電化學(xué)測試發(fā)現(xiàn)，在0.1C下，該材料的首次放電比容量為180.6mAh/g，庫倫效率為97.5%；2C時，比容量為71.0mAh/g，性能與傳統(tǒng)碳包覆Li2FeSiO4復(fù)合材料相當(dāng)。高的倍率容量主要?dú)w因于Li2FeSiO4特殊的等級結(jié)構(gòu)具有高的鋰離子擴(kuò)散動力學(xué)。 4.在等級梭形結(jié)構(gòu)的基礎(chǔ)之上，通過控制水熱反應(yīng)溫度和溶劑比例，獲得了一種新穎的、由單晶二維（2D）納米花瓣組裝而成的三維（3D）等級花形Li2FeSiO4材料。采用2-3nm厚度的石墨烯進(jìn)行表面包覆和電化學(xué)活化后，該復(fù)合材料的比容量高達(dá)327.2mAh/g，已接近兩個鋰離子的脫嵌，對應(yīng)的比能量為879Wh/kg，優(yōu)于傳統(tǒng)的Li2Mn2O4（487Wh/kg）和LiFePO4（500Wh/kg）材料。進(jìn)一步的倍率測試顯示，與目前報道的Li2FeSiO4材料性能相比，該復(fù)合材料在各個倍率下均具有較高的比容量。此外，經(jīng)200次高倍率循環(huán)后，其比容量保持率為92%左右。突出的電化學(xué)性能主要?dú)w因于Li2FeSiO4次級單晶納米花瓣在薄層方向上較短的鋰離子傳輸路徑，以及石墨烯包覆層的保護(hù)作用、鋰離子和電子的雙重輸運(yùn)作用等。
[Abstract]:New types of batteries and devices based on chemical energy / energy storage and conversion are the focus and focus of current scientific research. Lithium-ion batteries have the advantages of small mass, high storage capacity, long life, high safety performance and friendly environment. It has a wide application prospect in the field of energy storage and transformation. However, it is limited to traditional positive materials. Lower energy density and power density, lithium-ion batteries are difficult to meet the requirements of the next generation of high-end power battery equipment. The new type of silicate positive material has high theoretical ratio, rich resources, cheap price, and high safety performance. Among them, Li2FeSiO4 is getting more and more people because of its stable cycle performance. It has wide application prospects. However, the low conductivity and lithium ion diffusion kinetics of Li2FeSiO4 cathode materials limit its application.
In this paper, in view of the problems existing in the Li2FeSiO4 cathode material, through structural design and regulation, multi-dimensional nano Li2FeSiO4 lithium ion battery electrode materials with high specific capacity, long life and high ratio are prepared, and the following innovative research results are mainly obtained.
1. the zero dimension (0D) Li2FeSiO4 nanocrystalline / network carbon composite lithium ion battery cathode material was prepared by hydrothermal method and organic polymerization. Thanks to the excellent conductivity of the network carbon and the rapid transmission of nanocrystalline lithium ion, this novel composite material has 1.28 lithium ion inlaid specific capacity at the rate of 0.1C, which has realized from Fe2+ to Fe3+. The two continuous oxidation reactions to the Fe4+ have reached 189.8175.6148.9125.7 and 106.6mAh/g at the different ratios of 0.5,1,2,5 and 10C, and the specific capacity is still up to 175mAh/g. after a high rate of return to 1C, and the specific capacity is still up to 90.9mAh/g at the 10C ratio of 1000 times. The rate is 97.7%, with excellent multiplier cycle performance.
2. a one dimensional (1D) Li2FeSiO4 nanorod material was prepared by thermal reduction of a cheaper trivalent iron source. It was found that the single Li2FeSiO4 material was easily reunited in the process of charging and discharging, causing rapid attenuation of specific capacity. Therefore, a simple PVP anchoring method was used to anchor the nanorods on the graphene sheet and effectively suppress the nanorods. The reunion of active materials is made. Moreover, the graphene in it can also play an electronic transmission and relieve stress. The prepared nano rod like Li2FeSiO4/ graphene composite has excellent electrochemical properties: at the current density of 0.01A/g (1/16C) when the cathode material is charged between 1.5-4.8V as a lithium ion battery cathode material. The discharge specific capacity is 298mAh/g, and has high multiplier performance and long cycle life. When the anode material is charged and discharged between 0-3V as lithium ion battery, the initial discharge specific capacity at the current density of 0.02A/g (2/16C) is 1530mAh/g, the subsequent reversible capacity is 1160mAh/g, and the ratio performance and the cyclic stability performance are very sudden. Therefore, the use of graphene modified nano rod Li2FeSiO4 composite electrode material has excellent electrochemical performance, which is fully suitable for the needs of the next generation of power lithium ion batteries.
3. the Li2FeSiO4 material with a grade shuttle structure was prepared by the step hydrothermal method assisted by ethylene glycol. The study found that the spindle structure was made of single crystal nanoscale. The electrochemical test showed that the initial discharge ratio of the material was 180.6mAh/g and the efficiency of Kulun was 97.5% under 0.1C, and the specific capacity was 71.0mAh/g when 2C. Conventional carbon coated Li2FeSiO4 composites are equivalent. High rate capacity is mainly attributed to Li2FeSiO4 special hierarchical structure with high lithium ion diffusion kinetics.
4. on the basis of the grade shuttle structure, a novel, three dimensional (3D) grade Li2FeSiO4 material is obtained by controlling the temperature of the hydrothermal reaction and the proportion of solvent. The specific capacity of the composite is up to 327 after the surface coating and electrochemical activation of the 2-3nm thickness graphene. .2mAh/g, nearly two lithium ions have been deembedded, corresponding to the specific energy of 879Wh/kg, is better than the traditional Li2Mn2O4 (487Wh/kg) and LiFePO4 (500Wh/kg) materials. Further multiplier tests show that the composite has a higher specific capacity compared with the performance of the present reported Li2FeSiO4 materials at the rate of 200 times. After the ring, the specific capacity retention rate is about 92%. The outstanding electrochemical properties are mainly attributed to the short transport path of lithium ion in the thin layer of Li2FeSiO4 secondary single crystal, as well as the protective effect of the coating layer of graphene, the dual transport of lithium ion and electrons.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TM912

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