低熱固相反應(yīng)法制備水合磷酸鐵正極材料及其充放電性能研究
發(fā)布時(shí)間：2019-02-26 09:35
【摘要】：FePO4作為L(zhǎng)iFePO4的脫鋰化合物,其作為正極材料具有電壓適中、比容量高及熱穩(wěn)定性好等優(yōu)點(diǎn),因而有希望運(yùn)用在鋰離子電池中。目前制備FePO4的方法大都是液相沉淀和水熱法,其制備過程繁雜且難以得到純相的磷酸鐵。另外FePO4作為正極材料,由于本身晶體結(jié)構(gòu)的限制(電導(dǎo)率低和鋰離子擴(kuò)散性能差),從而導(dǎo)致其實(shí)際比容量不高且大電流放電性能差。本文針對(duì)以上問題做了以下三個(gè)方面的研究： 1.低熱固相反應(yīng)具有能耗低、污染少、選擇性高及不需要溶劑等優(yōu)點(diǎn),在無機(jī)納米材料制備領(lǐng)域占有重要地位。本文采用低熱固相反應(yīng)合成法,以FeCl3·6H2O作為鐵源,探究了Na3PO4·12H2O、Na2HPO4·12H2O及NaH2POa-2H20作為磷源制備磷酸鐵類材料的可行性。XRD結(jié)果表明當(dāng)P/Fe為1時(shí),只有選用Na2HPO4·12H2O作為P源,才能得到純相的具有晶型結(jié)構(gòu)的FePO4·2H2O。電化學(xué)測(cè)試同時(shí)表明該法制備的FePO·2H20無需任何處理就具有優(yōu)異的充放電循環(huán)性能,且效果優(yōu)于失去結(jié)晶水的FePO4。 2.以FeCl3·6H2O為鐵源,Na2HPO4·12H2O為磷源,系統(tǒng)研究了不同P/Fe比、不同陳化溫度、不同陳化時(shí)間、表面活性劑的添加對(duì)低熱固相反應(yīng)法制備FePO4·2H2O材料結(jié)構(gòu)、形貌及充放電性能的影響。XRD結(jié)果表明陳化時(shí)間對(duì)產(chǎn)物晶型結(jié)構(gòu)無顯著影響；而適當(dāng)增加P/Fe比和降低溫度,樣品趨向無定形化。表面活性劑的加入對(duì)樣品形貌影響很大。SEM測(cè)試表明加入PEG-6000后可制得球狀的FePO4·2H2O,該樣品整體放電比容量不高,但倍率性能優(yōu)異。 3.以二水合磷酸二氫鈉(NaH2POa·2H20)、六水合三氯化鐵(FeCl3·6H2O)及多壁碳納米管(MWNTs)為原料通過均相沉淀法合成FePO4·2H2O/MWNTs復(fù)合物。采用TG-DTA、XRD及IR分析了復(fù)合物的組成。TEM測(cè)試表明FePO4·2H2O粒徑在20 nm左右,并均勻的負(fù)載在MWNTs表面。充放電測(cè)試結(jié)果表明FePO4·2H2O/MWNTs復(fù)合物充放電性能遠(yuǎn)高于純相的FePO4·2H2O。以0.1 C充放電,首次放電比容量達(dá)到129.9 mAh·g-1,經(jīng)20次循環(huán)以后的容量仍保持在114.3 mAh·g-1,容量保持率接近90%。如此優(yōu)異的充放電性能歸因于FePO4·2H2O較小的粒徑縮短了Li+的擴(kuò)散路程,MWNTs的存在提高了FePO4·2H2O的導(dǎo)電性,同時(shí),MWNTs之間相互交錯(cuò)形成的三維導(dǎo)電網(wǎng)絡(luò)結(jié)構(gòu)有利于電解液的滲透。
[Abstract]:As a delithium compound of LiFePO4, FePO4, as a cathode material, has the advantages of moderate voltage, high specific capacity and good thermal stability, so it is promising to be used in lithium ion batteries. At present, most of the methods for preparing FePO4 are liquid phase precipitation and hydrothermal method. The preparation process is complicated and it is difficult to obtain pure phase iron phosphate. In addition, as a cathode material, due to the limitations of its crystal structure (low conductivity and poor lithium ion diffusion), the actual specific capacity of FePO4 is not high and the discharge performance of high current is poor. In this paper, the following three aspects of research on the above problems have been done: 1. Low-thermal solid-state reaction has the advantages of low energy consumption, less pollution, high selectivity and no need of solvent, so it plays an important role in the preparation of inorganic nano-materials. In this paper, using FeCl3 路6H2O as Tie Yuan, the feasibility of using Na3PO4 路12H2O, Na2HPO4 路12H2O and NaH2POa-2H20 as phosphorus sources to prepare iron phosphate materials was studied by low-temperature solid-state reaction method. The results show that when P/Fe is 1, The pure FePO4 路2H2O with crystal structure can be obtained only by using Na2HPO4 路12H2O as P source. Electrochemical measurements also show that the FePO 路2H20 prepared by this method has excellent charge / discharge cycle performance without any treatment, and the effect is better than that of FePO4. without crystal water. 2. Using FeCl3 路6H2O as Tie Yuan and Na2HPO4 路12H2O as phosphorus source, the structure of FePO4 路2H2O was systematically studied with different P/Fe ratio, different aging temperature, different aging time, and the addition of surfactant to low heat solid state reaction method. The results of XRD show that the aging time has no significant effect on the crystal structure of the product. However, when the P/Fe ratio is increased and the temperature is lowered, the sample tends to be amorphous. SEM results show that spherical FePO4 路2H2O can be prepared by addition of PEG-6000. The specific discharge capacity of the sample is not high, but the performance of the sample is excellent. 3. The FePO4 路2H2O / MWNTs composite was synthesized by homogeneous precipitation using sodium dihydrogen phosphate dihydrate (NaH2POa 路2H20), ferric chloride hexahydrate (FeCl3 路6H2O) and multi-walled carbon nanotubes (MWNTs) as raw materials. Tem test showed that the particle size of FePO4 路2H2O was about 20 nm and loaded uniformly on the surface of MWNTs. The composition of the composite was analyzed by TG-DTA,XRD and IR. The results of charge-discharge test show that the charge-discharge performance of FePO4 路2H2O / MWNTs composite is much higher than that of pure FePO4 路2H2O. At 0.1C, the initial discharge specific capacity reached 129.9 mAh 路g-1, and the capacity remained at 114.3 mAh 路g-1 after 20 cycles. The capacity retention rate was close to 90%. The excellent charge-discharge performance is due to the fact that the small particle size of FePO4 路2H2O shortens the diffusion path of Li, and the existence of MWNTs improves the conductivity of FePO4 路2H2O. At the same time, the structure of three-dimensional conductive network interlaced between MWNTs is beneficial to the permeation of electrolyte.
【學(xué)位授予單位】：南京師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2011
【分類號(hào)】：TM912
本文編號(hào)：2430654
[Abstract]:As a delithium compound of LiFePO4, FePO4, as a cathode material, has the advantages of moderate voltage, high specific capacity and good thermal stability, so it is promising to be used in lithium ion batteries. At present, most of the methods for preparing FePO4 are liquid phase precipitation and hydrothermal method. The preparation process is complicated and it is difficult to obtain pure phase iron phosphate. In addition, as a cathode material, due to the limitations of its crystal structure (low conductivity and poor lithium ion diffusion), the actual specific capacity of FePO4 is not high and the discharge performance of high current is poor. In this paper, the following three aspects of research on the above problems have been done: 1. Low-thermal solid-state reaction has the advantages of low energy consumption, less pollution, high selectivity and no need of solvent, so it plays an important role in the preparation of inorganic nano-materials. In this paper, using FeCl3 路6H2O as Tie Yuan, the feasibility of using Na3PO4 路12H2O, Na2HPO4 路12H2O and NaH2POa-2H20 as phosphorus sources to prepare iron phosphate materials was studied by low-temperature solid-state reaction method. The results show that when P/Fe is 1, The pure FePO4 路2H2O with crystal structure can be obtained only by using Na2HPO4 路12H2O as P source. Electrochemical measurements also show that the FePO 路2H20 prepared by this method has excellent charge / discharge cycle performance without any treatment, and the effect is better than that of FePO4. without crystal water. 2. Using FeCl3 路6H2O as Tie Yuan and Na2HPO4 路12H2O as phosphorus source, the structure of FePO4 路2H2O was systematically studied with different P/Fe ratio, different aging temperature, different aging time, and the addition of surfactant to low heat solid state reaction method. The results of XRD show that the aging time has no significant effect on the crystal structure of the product. However, when the P/Fe ratio is increased and the temperature is lowered, the sample tends to be amorphous. SEM results show that spherical FePO4 路2H2O can be prepared by addition of PEG-6000. The specific discharge capacity of the sample is not high, but the performance of the sample is excellent. 3. The FePO4 路2H2O / MWNTs composite was synthesized by homogeneous precipitation using sodium dihydrogen phosphate dihydrate (NaH2POa 路2H20), ferric chloride hexahydrate (FeCl3 路6H2O) and multi-walled carbon nanotubes (MWNTs) as raw materials. Tem test showed that the particle size of FePO4 路2H2O was about 20 nm and loaded uniformly on the surface of MWNTs. The composition of the composite was analyzed by TG-DTA,XRD and IR. The results of charge-discharge test show that the charge-discharge performance of FePO4 路2H2O / MWNTs composite is much higher than that of pure FePO4 路2H2O. At 0.1C, the initial discharge specific capacity reached 129.9 mAh 路g-1, and the capacity remained at 114.3 mAh 路g-1 after 20 cycles. The capacity retention rate was close to 90%. The excellent charge-discharge performance is due to the fact that the small particle size of FePO4 路2H2O shortens the diffusion path of Li, and the existence of MWNTs improves the conductivity of FePO4 路2H2O. At the same time, the structure of three-dimensional conductive network interlaced between MWNTs is beneficial to the permeation of electrolyte.
【學(xué)位授予單位】：南京師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2011
【分類號(hào)】：TM912
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