鐵基氧化物的制備與電極界面性能研究
發(fā)布時(shí)間：2018-09-04 10:16
【摘要】：簡(jiǎn)單過(guò)渡金屬氧化物如MnO2、α-Fe2O3、Fe3O4、Cr2O3、Co3O4、MnO、Cu2O因能提供高達(dá)700mAh/g以上的可逆容量而受到廣泛的關(guān)注，是極具潛力的新一代鋰離子電池電極材料。其中，鐵的氧化物（Fe2O3、Fe3O4）作為鋰離子電池負(fù)極材料因具有較高的理論比容量和廉價(jià)、環(huán)境友好等優(yōu)點(diǎn)受到較多的研究。但是鐵的氧化物導(dǎo)電性能較差和在充放電過(guò)程中體積變化較大，用作負(fù)極時(shí)出現(xiàn)很差的循環(huán)性能和倍率性能，進(jìn)而限制了鐵的氧化物作為負(fù)極材料的應(yīng)用。最常見(jiàn)的，也是最有效的解決方法是與碳材料進(jìn)行復(fù)合或者制備具有特殊形貌結(jié)構(gòu)的材料�；谝陨蟽牲c(diǎn)，本文通過(guò)將不同種類(lèi)的碳材料與鐵的氧化物進(jìn)行復(fù)合及制備特殊形貌結(jié)構(gòu)鐵的氧化物，旨在尋求此類(lèi)高能密度正極材料的改性方案；重點(diǎn)運(yùn)用電化學(xué)阻抗譜技術(shù)，探討電極動(dòng)力學(xué)過(guò)程及其電極界面的性能，尋求此類(lèi)電極的容量衰減的機(jī)理。主要研究?jī)?nèi)容和結(jié)果如下： （1）利用高溫固相反應(yīng)法制備α-Fe2O3/C復(fù)合材料。運(yùn)用X射線衍射（XRD）、掃描電子顯微鏡、充放電測(cè)試、電化學(xué)阻抗譜對(duì)其結(jié)構(gòu)和電化學(xué)性能進(jìn)行了表征。充放電測(cè)試結(jié)果顯示，α-Fe2O3/C電極循環(huán)50周時(shí)可逆充電容量為935.3mAh/g，循環(huán)性能較商品化α-Fe2O3有顯著改善。電化學(xué)阻抗譜測(cè)試結(jié)果顯示，α-Fe2O3/C電極在首次嵌鋰過(guò)程中分別出現(xiàn)了鋰離子通過(guò)固體電解質(zhì)相界面膜（SEI膜）的遷移、材料的電子電導(dǎo)率、電荷傳遞過(guò)程相關(guān)的半圓，并詳細(xì)分析了它們的變化規(guī)律。 （2）采用水熱合成的方法分別制備了α-Fe2O3/GNS、α-Fe2O3/CNTs復(fù)合材料和亞微米顆粒α-Fe2O3，系統(tǒng)研究了不同碳源對(duì)α-Fe2O3的形貌、結(jié)構(gòu)和電化學(xué)性能影響。測(cè)試結(jié)果表明，α-Fe2O3/GNS和α-Fe2O3/CNTs電極有較高的可逆容量、倍率性能及在大電流下較長(zhǎng)的循環(huán)壽命。復(fù)合材料電化學(xué)性能的提高歸結(jié)于三個(gè)方面：一方面碳材料可以緩解由體積變化產(chǎn)生的應(yīng)力及活性顆粒團(tuán)聚現(xiàn)象；另一方面，復(fù)合材料具有的較大的表面積，使得電極/電解液接觸充分；此外，碳材料可以提高電極的電子電導(dǎo)率。 （3）采用水熱法制備了空心納米結(jié)構(gòu)的α-Fe2O3。隨著反應(yīng)時(shí)間的延長(zhǎng)，α-Fe2O3出現(xiàn)了從棒狀到管狀的演變過(guò)程。通過(guò)對(duì)這一系列產(chǎn)物進(jìn)行表征，得出管狀的形成是由棒狀從兩端開(kāi)始“溶解”再結(jié)晶的過(guò)程，且“溶解”的方向是沿著[001]晶向指數(shù)（C軸）。采用了不同反應(yīng)物濃度（PO43-）制備α-Fe2O3，隨著PO43-濃度的減少，α-Fe2O3出現(xiàn)了從桶狀到環(huán)狀的演變過(guò)程。通過(guò)對(duì)這一系列產(chǎn)物進(jìn)行表征，得出陰離子（PO43-和SO42-）對(duì)產(chǎn)物形貌的調(diào)控作用是有所差別的。即，PO43-易于控制前驅(qū)體生長(zhǎng)，SO42-更傾向于加速α-Fe2O3的“溶解”過(guò)程。對(duì)所制備的α-Fe2O3進(jìn)行了電化學(xué)性能測(cè)試，表明管狀的α-Fe2O3有最好的電化學(xué)性能。經(jīng)過(guò)65周循環(huán)之后，納米管狀的α-Fe2O3電極可逆容量為1131mAh/g，容量保持率在83%。且在不同充放電電流下，管狀的α-Fe2O3具有較好可逆容量和倍率性能，這與其特殊結(jié)構(gòu)密切相關(guān)。 （4）采用水熱法制備了Fe@Fe2O3核殼納米顆粒與GNS、CNTs復(fù)合材料，F(xiàn)e@Fe2O3/GNS電極在100mA/g下經(jīng)過(guò)90周循環(huán)后，仍有959.3mAh/g的可逆容量，容量保持率在86.4%。在大電流密度下，經(jīng)過(guò)280周循環(huán)后，F(xiàn)e@Fe2O3/GNS電極的可逆容量仍然有515mAh/g。電化學(xué)阻抗譜測(cè)試結(jié)果顯示，在首次嵌鋰過(guò)程中，EIS的Nyquist圖出現(xiàn)三個(gè)半圓，即高頻區(qū)域的一個(gè)圓弧(HFA)，中頻區(qū)域的一個(gè)半圓(MFS)和低頻區(qū)域的一個(gè)半圓(LFS)，，并對(duì)每部分的歸屬進(jìn)行了探討，詳細(xì)分析了它們的變化規(guī)律。 在100mA/g下經(jīng)過(guò)60周循環(huán)后，F(xiàn)e@Fe2O3/CNTs電極仍有702.7mAh/g的可逆容量。Fe@Fe2O3/CNTs電極具有較好的倍率性能，且在大電流充放電下，仍然具有較好的可逆容量。電化學(xué)阻抗譜測(cè)試結(jié)果顯示，金屬Fe和CNTs的存在有利于降低鋰離子通過(guò)SEI膜和電荷傳遞電阻，進(jìn)而使得Fe@Fe2O3/CNTs復(fù)合材料具有較好的電化學(xué)性能。 （5）采用溶劑熱合成的方法合成了Fe3O4-HSs和Fe3O4-HSs/CNTs復(fù)合材料。在100mA/g下，F(xiàn)e3O4-HSs/CNTs電極循環(huán)70周后，可逆容量高達(dá)1153.8mAh/g，容量保存率在87.8%；在10.0A/g大電流下，F(xiàn)e3O4-HSs/CNTs電極經(jīng)過(guò)350周長(zhǎng)周期循環(huán)后，可逆容量仍然能夠保持在552.7mAh/g。 采用水熱、固相燒結(jié)的合成方法分別制備了Fe3O4/CNTs和Fe3O4/C復(fù)合材料。充放電測(cè)試顯示：Fe3O4/CNTs、Fe3O4/C和商品化Fe3O4電極的首次放電容量分別為1421mAh/g、1651mAh/g和2104mAh/g，循環(huán)到55周時(shí)可逆容量分別為1030mAh/g、513mAh/g和280mAh/g。EIS測(cè)試表明，F(xiàn)e3O4/CNTs電極在首次放電過(guò)程中，出現(xiàn)了高頻區(qū)域與SEI膜相關(guān)的一個(gè)半圓，中頻區(qū)域與電荷傳遞過(guò)程相關(guān)的一個(gè)半圓，低頻區(qū)域與相變電阻相關(guān)的一個(gè)圓弧。
[Abstract]:Simple transition metal oxides such as MnO2, alpha-Fe2O3, Fe3O4, Cr2O3, Co3O4, MnO and Cu2O have attracted much attention because they can provide reversible capacities up to 700 mAh/g. They are potential electrode materials for lithium-ion batteries. Among them, iron oxides (Fe2O3, Fe3O4) have high theoretical specific capacities as anode materials for lithium-ion batteries. However, the poor conductivity of iron oxides and the large volume change during charging and discharging process lead to poor cycling and rate performance when used as negative electrode, which limits the application of iron oxides as negative electrode materials. Based on the above two points, in this paper, different kinds of carbon materials are compounded with iron oxides and iron oxides with special morphology are prepared. The purpose of this paper is to find the modification scheme of this kind of high energy density cathode materials. The dynamic process of the electrode and the performance of the electrode interface are discussed, and the mechanism of capacity decay of the electrode is explored.
(1) Alpha-Fe2O3/C composites were prepared by high-temperature solid-state reaction method. The structure and electrochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge test and electrochemical impedance spectroscopy (EIS). The electrochemical impedance spectroscopy (EIS) results show that there are lithium ions migrating through the solid electrolyte phase interfacial film (SEI film) during the first lithium intercalation, the electronic conductivity of the material and the semicircle related to the charge transfer process.
(2) Alpha-Fe2O3/GNS, alpha-Fe2O3/CNTs composites and submicron particles of alpha-Fe2O3 were synthesized by hydrothermal method. The effects of different carbon sources on the morphology, structure and electrochemical properties of alpha-Fe2O3 were studied systematically. The improvement of the electrochemical properties of the composites can be attributed to three aspects: on the one hand, carbon materials can alleviate the stress caused by volume change and agglomeration of active particles; on the other hand, the large surface area of the composites makes the electrode/electrolyte contact fully; on the other hand, carbon materials can improve the electrode performance. Electronic conductivity.
(3) Alpha-Fe2O3 hollow nanostructures were synthesized by hydrothermal method. With the extension of reaction time, the evolution from rod-like to tubular morphology of alpha-Fe2O3 was observed. Index (C axis). Alpha-Fe2O3 was prepared with different PO43 -. With the decrease of PO43 -, a process from barrel-like to ring-like appeared in the formation of alpha-Fe2O3. SO42-tends to accelerate the "dissolution" of alpha-Fe2O3. The electrochemical properties of the prepared alpha-Fe2O3 were tested and the results show that the tube-like alpha-Fe2O3 has the best electrochemical performance. After 65 weeks of cycling, the reversible capacity of the nanotube-like alpha-Fe2O3 electrode is 1131 mAh/g, and the capacity retention rate is 83%. The -Fe2O3 has good reversible capacity and multiplying property, which is closely related to its special structure.
(4) Fe@Fe2O3 core-shell nanoparticles and GNS, CNTs composites were prepared by hydrothermal method. After 90 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/GNS electrode was 959.3 mAh/g and the capacity retention rate was 86.4%. At high current density, after 280 weeks of cycling, the reversible capacity of Fe@Fe2O3/GNS electrode was 515 mAh/g. The results show that in the first lithium insertion process, three semicircles appear in the Nyquist diagram of EIS, namely, an arc in the high frequency region (HFA), a semicircle in the intermediate frequency region (MFS) and a semicircle in the low frequency region (LFS). The attribution of each part is discussed and their changing rules are analyzed in detail.
After 60 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/CNTs electrode was still 702.7 mAh/g. Fe@Fe2O3/CNTs electrode had good rate-doubling performance, and still had good reversible capacity at high current charge-discharge. The results of EIS showed that the presence of Fe and CNTs was beneficial to the reduction of lithium ion passing through SEI film and electrochemistry. The charge transfer resistance makes Fe@Fe2O3/CNTs composites have better electrochemical performance.
(5) Fe3O4-HSs and Fe3O4-HSs/CNTs composites were synthesized by solvothermal synthesis. After 70 weeks of cycling at 100 mA/g, the reversible capacity of the Fe3O4-HSs/CNTs electrode was as high as 1153.8 mAh/g, and the capacity retention rate was 87.8%. At 10.0A/g high current, the reversible capacity of the Fe3O4-HSs/CNTs electrode remained at 552.7 m after 350 cycles. Ah/g.
Fe_3O_4/CNTs and Fe_3O_4/C composites were synthesized by hydrothermal and solid-phase sintering methods. Charge and discharge tests showed that the first discharge capacities of Fe_3O_4/CNTs, Fe_3O_4/C and commercialized Fe_3O_4 electrodes were 1421 mAh/g, 1651 mAh/g and 2104 mAh/g, respectively. The reversal capacities were 1030 mAh/g, 513 mAh/g and 280 mAh/g. EIS at 55 weeks. During the first discharge of the Fe_3O_4/CNTs electrode, a semicircle in the high frequency region related to the SEI film, a semicircle in the middle frequency region related to the charge transfer process, and an arc in the low frequency region related to the phase change resistance.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TM912.9
本文編號(hào)：2221787
[Abstract]:Simple transition metal oxides such as MnO2, alpha-Fe2O3, Fe3O4, Cr2O3, Co3O4, MnO and Cu2O have attracted much attention because they can provide reversible capacities up to 700 mAh/g. They are potential electrode materials for lithium-ion batteries. Among them, iron oxides (Fe2O3, Fe3O4) have high theoretical specific capacities as anode materials for lithium-ion batteries. However, the poor conductivity of iron oxides and the large volume change during charging and discharging process lead to poor cycling and rate performance when used as negative electrode, which limits the application of iron oxides as negative electrode materials. Based on the above two points, in this paper, different kinds of carbon materials are compounded with iron oxides and iron oxides with special morphology are prepared. The purpose of this paper is to find the modification scheme of this kind of high energy density cathode materials. The dynamic process of the electrode and the performance of the electrode interface are discussed, and the mechanism of capacity decay of the electrode is explored.
(1) Alpha-Fe2O3/C composites were prepared by high-temperature solid-state reaction method. The structure and electrochemical properties of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge test and electrochemical impedance spectroscopy (EIS). The electrochemical impedance spectroscopy (EIS) results show that there are lithium ions migrating through the solid electrolyte phase interfacial film (SEI film) during the first lithium intercalation, the electronic conductivity of the material and the semicircle related to the charge transfer process.
(2) Alpha-Fe2O3/GNS, alpha-Fe2O3/CNTs composites and submicron particles of alpha-Fe2O3 were synthesized by hydrothermal method. The effects of different carbon sources on the morphology, structure and electrochemical properties of alpha-Fe2O3 were studied systematically. The improvement of the electrochemical properties of the composites can be attributed to three aspects: on the one hand, carbon materials can alleviate the stress caused by volume change and agglomeration of active particles; on the other hand, the large surface area of the composites makes the electrode/electrolyte contact fully; on the other hand, carbon materials can improve the electrode performance. Electronic conductivity.
(3) Alpha-Fe2O3 hollow nanostructures were synthesized by hydrothermal method. With the extension of reaction time, the evolution from rod-like to tubular morphology of alpha-Fe2O3 was observed. Index (C axis). Alpha-Fe2O3 was prepared with different PO43 -. With the decrease of PO43 -, a process from barrel-like to ring-like appeared in the formation of alpha-Fe2O3. SO42-tends to accelerate the "dissolution" of alpha-Fe2O3. The electrochemical properties of the prepared alpha-Fe2O3 were tested and the results show that the tube-like alpha-Fe2O3 has the best electrochemical performance. After 65 weeks of cycling, the reversible capacity of the nanotube-like alpha-Fe2O3 electrode is 1131 mAh/g, and the capacity retention rate is 83%. The -Fe2O3 has good reversible capacity and multiplying property, which is closely related to its special structure.
(4) Fe@Fe2O3 core-shell nanoparticles and GNS, CNTs composites were prepared by hydrothermal method. After 90 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/GNS electrode was 959.3 mAh/g and the capacity retention rate was 86.4%. At high current density, after 280 weeks of cycling, the reversible capacity of Fe@Fe2O3/GNS electrode was 515 mAh/g. The results show that in the first lithium insertion process, three semicircles appear in the Nyquist diagram of EIS, namely, an arc in the high frequency region (HFA), a semicircle in the intermediate frequency region (MFS) and a semicircle in the low frequency region (LFS). The attribution of each part is discussed and their changing rules are analyzed in detail.
After 60 weeks of cycling at 100 mA/g, the reversible capacity of Fe@Fe2O3/CNTs electrode was still 702.7 mAh/g. Fe@Fe2O3/CNTs electrode had good rate-doubling performance, and still had good reversible capacity at high current charge-discharge. The results of EIS showed that the presence of Fe and CNTs was beneficial to the reduction of lithium ion passing through SEI film and electrochemistry. The charge transfer resistance makes Fe@Fe2O3/CNTs composites have better electrochemical performance.
(5) Fe3O4-HSs and Fe3O4-HSs/CNTs composites were synthesized by solvothermal synthesis. After 70 weeks of cycling at 100 mA/g, the reversible capacity of the Fe3O4-HSs/CNTs electrode was as high as 1153.8 mAh/g, and the capacity retention rate was 87.8%. At 10.0A/g high current, the reversible capacity of the Fe3O4-HSs/CNTs electrode remained at 552.7 m after 350 cycles. Ah/g.
Fe_3O_4/CNTs and Fe_3O_4/C composites were synthesized by hydrothermal and solid-phase sintering methods. Charge and discharge tests showed that the first discharge capacities of Fe_3O_4/CNTs, Fe_3O_4/C and commercialized Fe_3O_4 electrodes were 1421 mAh/g, 1651 mAh/g and 2104 mAh/g, respectively. The reversal capacities were 1030 mAh/g, 513 mAh/g and 280 mAh/g. EIS at 55 weeks. During the first discharge of the Fe_3O_4/CNTs electrode, a semicircle in the high frequency region related to the SEI film, a semicircle in the middle frequency region related to the charge transfer process, and an arc in the low frequency region related to the phase change resistance.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TM912.9
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