本文選題：富鋰正極材料 + 層狀-尖晶石復(fù)合結(jié)構(gòu)��； 參考：《湘潭大學(xué)》2016年碩士論文

【摘要】：富鋰正極材料作為目前鋰離子電池正極材料的主流發(fā)展方向之一,具有放電比容量高、成本低廉、環(huán)境友好等特點(diǎn),從其首次被報(bào)道至今,一直受到廣泛關(guān)注。然而,材料本身存在著的循環(huán)穩(wěn)定性差、首次庫倫效率低、倍率性能差、尤其是電壓平臺衰減快等缺點(diǎn)一直都是研究人員關(guān)注的重點(diǎn)。本論文的主要目的是為富鋰正極材料的改性研究提供一種新的思路、在電池的綜合性能方面做出改進(jìn),因此,設(shè)計(jì)并制備了一種具有層狀-尖晶石復(fù)合結(jié)構(gòu)的富鋰正極材料。論文從制備方法、結(jié)構(gòu)特點(diǎn)、工藝條件的影響及電化學(xué)性能的改性幾個方面對該復(fù)合結(jié)構(gòu)富鋰正極材料進(jìn)行了系統(tǒng)的研究。論文的具體研究內(nèi)容如下:1.采用溶劑熱法和后續(xù)梯度煅燒法制備了具有層狀-尖晶石復(fù)合結(jié)構(gòu)的富鋰正極材料。該復(fù)合材料內(nèi)部同時具有層狀的Li2MnO3相和尖晶石型Li4Mn5O12相。尖晶石型的Li4Mn5O12相結(jié)構(gòu)內(nèi)部具有3D孔徑,能夠?yàn)長i離子的傳輸提供更加自由的空間;而層狀Li2MnO3相的存在則保證了材料具有較高的比容量。通過研究證明,該復(fù)合結(jié)構(gòu)中兩相的存在可以相得益彰,既保證材料具有較高的實(shí)際比容量,同時又改善了材料的循環(huán)性能和結(jié)構(gòu)穩(wěn)定性。在2.0-4.6 V的電壓范圍內(nèi),首次制備的層狀-尖晶石復(fù)合結(jié)構(gòu)富鋰正極材料在0.1 C下的放電比容量為289.6 mAh/g,在10 C下的放電比容量為122.8 mAh/g;同時,在0.5 C條件下,該層狀-尖晶石復(fù)合結(jié)構(gòu)富鋰正極材料循環(huán)200次后的容量保持率達(dá)到了88%。2.基于前面的研究,對層狀-尖晶石復(fù)合結(jié)構(gòu)正極材料制備方法中的實(shí)驗(yàn)條件進(jìn)行對比與分析,以確定影響復(fù)合結(jié)構(gòu)中兩相組成比例的實(shí)驗(yàn)條件及其影響結(jié)果,同時通過對具有不同組成的樣品其電化學(xué)性能的比較,確定了具有最優(yōu)電化學(xué)性能的相組成比例。研究結(jié)果表明,后續(xù)高溫固相反應(yīng)過程中的煅燒溫度和時間共同影響著材料的結(jié)構(gòu)組成:(1)當(dāng)煅燒溫度在750℃時,結(jié)構(gòu)中主要生成的是尖晶石型Li4Mn5O12相,當(dāng)煅燒溫度在800℃時,結(jié)構(gòu)中則主要生成層狀Li2MnO3相;(2)當(dāng)在750℃下的煅燒時間超過10 h時,材料中才開始出現(xiàn)尖晶石型Li4Mn5O12相,與此同時,隨著在800℃下煅燒時間的增加,結(jié)構(gòu)中已生成的尖晶石相會逐漸轉(zhuǎn)化成層狀相。3.為了解決層狀-尖晶石復(fù)合結(jié)構(gòu)富鋰正極材料導(dǎo)電性差的問題,在前面的研究基礎(chǔ)之上,設(shè)計(jì)并制備了聚苯胺包覆的層狀-尖晶石復(fù)合結(jié)構(gòu)富鋰正極材料。研究表明,聚苯胺的包覆在不改變材料內(nèi)部復(fù)合結(jié)構(gòu)的基礎(chǔ)上,有效地提高了該正極材料的導(dǎo)電性,大大降低了材料在循環(huán)過程中的阻抗;同時,該聚苯胺包覆的復(fù)合結(jié)構(gòu)富鋰正極材料在0.1 C,2.0-4.6 V條件下的首次放電比容量為302.9 mAh/g,首次庫倫效率為83.5%,10 C倍率下的放電比容量為146.2 mAh/g,0.5C條件下循環(huán)200次后的容量保持率可以達(dá)到92.4%。4.為了進(jìn)一步改善富鋰正極材料的電化學(xué)性能,將前面幾章中采用的溶劑熱法運(yùn)用到其他富鋰正極材料上,制備出粒徑均一、分散性好的微球,粒子直徑控制在1μm左右。并在此基礎(chǔ)上,采用Na摻雜和多孔結(jié)構(gòu)的雙向設(shè)計(jì)對正極材料進(jìn)行改性。研究結(jié)果表明,富鋰正極材料的粒子直徑控制在1μm,同時在材料內(nèi)部進(jìn)行Na摻雜,利用Na離子半徑和過渡金屬離子半徑之間的差距,可以擴(kuò)大Li層之間的晶格間距,從而增加結(jié)構(gòu)的穩(wěn)定性;此外,正極微球中的多孔結(jié)構(gòu)可以在保證材料具有良好的振實(shí)密度和結(jié)構(gòu)穩(wěn)定性的同時,增加電極與電解液之間的接觸面積,同時為Li離子的存儲提供更多的空位。最終制備的Na摻雜富鋰多孔正極微球,其在0.1 C,2.0-4.6 V條件下的首次放電比容量為305.3mAh/g,在0.5 C、5 C、10 C下的放電比容量分別為252.3 mAh/g、200.8 mAh/g、177.2 mAh/g。
[Abstract]:As one of the mainstream development direction of lithium ion battery cathode materials, lithium rich cathode materials have been widely concerned because of their high discharge specific capacity, low cost and friendly environment. However, the circulation stability of the material itself is poor, the efficiency of the first Kulun is low, and the performance is poor, especially the electricity. The main purpose of this paper is to provide a new way of thinking for the study of the modification of lithium rich cathode materials and to improve the comprehensive performance of the batteries. Therefore, a kind of lithium rich cathode material with layered spinel Shi Fuhe structure is designed and prepared. The preparation methods, the structural characteristics, the influence of the technological conditions and the modification of the electrochemical properties are systematically studied. The specific contents of this paper are as follows: 1. the lithium rich cathode material with lamellar crystal composite structure was prepared by the solvent thermal method and the follow up calcining method. The Li2MnO3 phase and spinel type Li4Mn5O12 phase in the material are at the same time. The Li4Mn5O12 phase structure of the spinel type has a 3D aperture, which can provide more free space for the transmission of Li ions, while the existence of the layered Li2MnO3 phase ensures a higher specific capacity of the material. Through the study, the existence of two phases in the composite structure has been proved. It can not only guarantee the material with higher actual specific capacity, but also improve the cyclic performance and structural stability of the material. In the range of 2.0-4.6 V voltage, the discharge specific capacity of the first prepared layered spinel composite cathode material under 0.1 C is 289.6 mAh/g, and the discharge specific capacity under 10 C is 122.8 mAh At the same time, under the condition of 0.5 C, the capacity retention rate of the lamellar spinel composite cathode material after 200 cycles reached the previous study. The experimental conditions of the preparation method of the layered spinel composite positive material were compared and analyzed to determine the experiment on the proportion of the two phase composition in the composite structure. The results show that the phase composition with the optimal electrochemical performance is determined by comparison of the electrochemical properties of the samples with different composition. The results show that the calcining temperature and time in the subsequent high temperature solid state reaction affect the structure composition of the material together: (1) when the calcining temperature is at 750. The main formation of the spinel Li4Mn5O12 phase is the Li4Mn5O12 phase. When the calcining temperature is at 800 C, the structure is mainly formed in the layered Li2MnO3 phase. (2) the spinel Li4Mn5O12 phase begins to appear when the calcining time is over 10 h at 750 C. At the same time, with the increase of calcining time at 800 C, the spinel in the structure has been formed. In order to solve the problem of poor conductivity of the lithium rich cathode material in layered spinel composite structure, the phase.3. has been designed and prepared on the basis of the previous research. The study shows that the coating of polyaniline is not changed in the composite structure of the material. On the basis, the conductivity of the cathode material is effectively improved and the impedance of the material in the cycle process is greatly reduced. At the same time, the first discharge specific capacity of the polyaniline coated composite lithium cathode material at 0.1 C and 2.0-4.6 V is 302.9 mAh/g, the first Kulun efficiency is 83.5%, and the discharge specific capacity under the 10 C ratio is 146.2 mAh. /g, 0.5C under the condition of 200 cycles, the capacity retention rate can reach 92.4%.4. in order to further the electrochemical performance of the Gai Shanfu lithium cathode material. The solvent thermal method used in the previous chapters is applied to other lithium rich cathode materials to prepare the microspheres with homogeneous particle size and good dispersion, and the particle diameter is controlled at about 1 m. The positive electrode materials are modified by Na doping and porous structure. The results show that the particle diameter of the lithium rich cathode material is controlled at 1 u m and Na doping in the material. The gap between the Na ion radius and the transition metal ion radius can be used to enlarge the lattice spacing between the Li layers, thus increasing the structure. In addition, the porous structure in the positive microspheres can increase the contact area between the electrode and the electrolyte while ensuring that the material has good vibrational density and structural stability, and provides more vacancy for the storage of Li ions. The final preparation of Na doped lithium rich porous cathode microspheres is under the condition of 0.1 C and 2.0-4.6 V. The first discharge specific capacity is 305.3mAh/g, and the discharge capacity at 0.5 C, 5 C, and 10 C is 252.3 mAh/g, 200.8 mAh/g, 177.2 mAh/g., respectively.
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TM912

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