【摘要】：正交橄欖石型LiFePO_4材料具有理論容量高(170 m Ahg-1),環(huán)境友好,熱穩(wěn)定性能好,循環(huán)性能高(超過2000次),原料豐富,成本低等優(yōu)勢,是具有極大應(yīng)用前景的鋰離子電池正極材料,已經(jīng)得到了廣泛的應(yīng)用。但是LiFePO_4固有的缺陷是電子導(dǎo)電率和鋰離子擴散速率都很低,嚴(yán)重影響材料實際容量及倍率性能的發(fā)揮。本論文采用廉價的工業(yè)原料合成納米LiFePO_4,具體研究內(nèi)容如下:首先以廢鐵水為鐵源,磷酸氫二銨為磷源,檸檬酸作為表面活性劑,研究納米Fe PO_4的制備。作為對比試驗,將添加不同質(zhì)量檸檬酸制備的Fe PO_4分別命名為FP-A(0 g檸檬酸),FP-B(0.2 g檸檬酸),FP-C(0.4 g檸檬酸)和FP-D(0.6 g檸檬酸)。用掃描電子顯微鏡(SEM)和傅里葉變換紅外光譜(FTIR)分別研究了Fe PO_4的尺寸形貌和表面特性。測試表明,Fe PO_4尺寸隨檸檬酸量的增加而減小。FP-D的尺寸分布在納米級,團(tuán)聚少;采用前驅(qū)體Fe PO_4,碳酸鋰,蔗糖為原材料,通過碳熱還原法合成LiFePO_4/C正極材料。作為對比試驗,分別由FP-A,FP-B,FP-C和FP-D合成的LiFePO_4/C命名為LFP-A,LFP-B,LFP-C和LFP-D。用X射線衍射(XRD),SEM,電池恒流充放電分別研究了正極材料的結(jié)構(gòu),尺寸形貌及電化學(xué)性能。測試表明,Fe PO_4的尺寸形貌對LiFePO_4/C產(chǎn)生影響,Fe PO_4的尺寸越小、形貌越規(guī)則,LiFePO_4/C正極材料的尺寸就越小、團(tuán)聚少。在0.1 C倍率下測試表明,檸檬酸的加入不利于LiFePO_4/C材料放電容量提高,但是會減小正極材料的極化和容量衰減,提高倍率循環(huán)性能。采用不同含量的金屬Mn~(2+)離子(0%,5%,8%和10%)對LiFePO_4材料進(jìn)行摻雜。用XRD,SEM,電池恒流充放電研究了不同含量金屬摻雜正極材料的結(jié)構(gòu),尺寸形貌及電化學(xué)特性。測試表明,采用Mn~(2+)摻雜并不會影響正極材料的結(jié)構(gòu),當(dāng)Mn~(2+)摻雜量為5%的Li Fe0.95Mn0.05PO_4正極材料在0.1 C倍率下首次放電容量最高。采用循環(huán)伏安(CV)法和電化學(xué)阻抗譜(EIS)研究了Mn~(2+)摻雜對正極材料電極動力學(xué)及鋰離子傳輸?shù)挠绊憽?br/>[Abstract]:Orthogonal olivine LiFePO_4 has the advantages of high theoretical capacity (170m Ahg-1), friendly environment, good thermal stability, high cycle performance (more than 2000 times), rich raw materials and low cost. It is a promising cathode material for lithium-ion batteries and has been widely used. However, the inherent defect of LiFePO_4 is that the electronic conductivity and lithium ion diffusion rate are very low, which seriously affects the actual capacity and rate performance of the material. In this paper, the synthesis of nano-LiFePO_4, from cheap industrial raw materials is as follows: firstly, the preparation of nano-FePO_4 was studied by using waste molten iron as Tie Yuan, diammonium hydrogen phosphate as phosphorus source and citric acid as surfactants. As a comparative experiment, the Fe PO_4 prepared by adding different mass citric acid was named FP-A (0 g citric acid) and FP-B (0.2 g citric acid), respectively. FP-C (0.4g citric acid) and FP-D (0.6g citric acid). The size, morphology and surface properties of Fe PO_4 were studied by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results show that the size of Fe PO_4 decreases with the increase of citric acid content. The size of FP-D is distributed in nanometer scale and the agglomeration is less. LiFePO_4/C cathode materials were synthesized by carbothermal reduction using precursor FePO_4, lithium carbonate and sucrose as raw materials. As a comparative experiment, the LiFePO_4/C synthesized by FP-A,FP-B,FP-C and FP-D is named LFP-A,LFP-B,LFP-C and LFP-D., respectively. The structure, size and electrochemical properties of cathode materials were studied by X-ray diffraction (XRD) (XRD), SEM, battery at constant current charge and discharge. The results show that the size and morphology of FePO_4 have an effect on LiFePO_4/C. The smaller the size of FePO_4, the more regular the morphology, the smaller the size of LiFePO_4/C cathode material and the less agglomeration. The test results at 0.1 C rate show that the addition of citric acid is not conducive to the increase of discharge capacity of LiFePO_4/C materials, but it can reduce the polarization and capacity attenuation of cathode materials and improve the rate cycle performance. Different contents of metal Mn~ (2) ions (0%, 5%, 8% and 10%) were used to doping LiFePO_4 materials. The structure, size, morphology and electrochemical characteristics of metal-doped cathode materials with different contents were studied by constant current charge-discharge of XRD,SEM, battery. The results show that the structure of the cathode material is not affected by Mn~ (2) doping, and the first discharge capacity of the Li Fe0.95Mn0.05PO_4 cathode material with Mn~ (2) doping content of 5% is the highest at 0.1 C rate. The effects of Mn~ (2) doping on electrode kinetics and lithium ion transport of cathode materials were studied by cyclic volt-ampere (CV) and electrochemical impedance spectroscopy (EIS).
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM912

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