發(fā)布時(shí)間：2018-06-20 19:30

  本文選題：鋰離子電池 + 富鋰材料�。� 參考：《哈爾濱工業(yè)大學(xué)》2016年碩士論文

【摘要】：鋰離子電池富鋰錳基正極材料xLi2MnO3·(1-x)LiMO2具有比能量高、循環(huán)壽命長、安全性能好等優(yōu)點(diǎn),使其成為動(dòng)力電池的理想正極材料之一。本文以層狀富鋰錳基正極材料Li1.2Mn0.54Ni0.13Co0.13O2為研究對(duì)象,分別采用共沉淀法(CP)和溶膠凝膠法(SG)制備出目標(biāo)材料,通過XRD、SEM、CV、EIS和恒流充放電測試等手段,深入研究了材料的晶體結(jié)構(gòu)、物理形貌和電化學(xué)性能。首先,對(duì)共沉淀法制備工藝中的沉淀pH值,鋰源的選擇,煅燒時(shí)間以及煅燒溫度進(jìn)行了探索和優(yōu)化,得出最佳工藝為:以乙酸鹽為原料,NaOH和NH4?H2O為沉淀劑,在pH=11.0條件下得到氫氧化物前驅(qū)體,在氫氧化物前驅(qū)體中加入LiOH?H2O為鋰源,500℃預(yù)燒5h,900℃空氣氣氛中燒結(jié)12h得到目標(biāo)材料。材料的首次放電比容量(0.5C,1C=300mA/g)為283.1mAh/g,庫倫效率高達(dá)80.7%,在0.2C下循環(huán)50周材料的放電比容量為179.5mAh/g,容量保持率為76.7%,在1.0C下循環(huán)100周材料的放電比容量為118.9mAh/g,容量保持率為73.3%,2.0C下材料的放電比容量仍有為108.2mAh/g。為了改善材料的循環(huán)穩(wěn)定性和倍率性能,采用MoO3和Al2O3對(duì)材料分別進(jìn)行包覆改性。MoO3包覆最佳比例為1%,此材料的首次放電比容量(0.5C)為256.7mAh/g,庫倫效率高達(dá)83.4%,在1.0C下循環(huán)100周材料的放電比容量為107.3mAh/g,容量保持率分別為78.4%;Al2O3包覆最佳比例為5%,在1.0C下循環(huán)100周材料的容量保持率高達(dá)87.8%。包覆層減少了電解液對(duì)活性材料的腐蝕,循環(huán)穩(wěn)定性提高。對(duì)共沉淀法制備的材料進(jìn)行充放電機(jī)制的探究,得出結(jié)論為:最佳充電截止電壓為4.6V,此電壓下可以減少電解液的分解,抑制對(duì)活性材料的腐蝕,而將電池恒流恒壓充至電流衰減至原來的1/20為最佳充電截止電流。其次,采用溶膠凝膠法制備材料Li1.2Mn0.54Ni0.13Co0.13O2,最佳工藝為:以乙酸鹽為原料,乙醇酸為絡(luò)合劑(乙醇酸:金屬離子=1.0),采用氨水調(diào)節(jié)pH在7.0~8.0之間,450℃預(yù)燒5h,900℃空氣氣氛中燒結(jié)12h得到目標(biāo)材料Li1.2Mn0.54Ni0.13Co0.13O2。材料的首次放電比容量(0.5C)為275.9mAh/g,庫倫效率高達(dá)74.0%,在0.2C下循環(huán)100周材料的放電比容量為81.3mAh/g,容量保持率為39.4%,溶膠凝膠法合成的材料具有較好的層狀結(jié)構(gòu)以及材料的分散性好,活性物質(zhì)得以充分利用,且材料分散性較好,比表面積大,Li+可實(shí)現(xiàn)快速脫嵌,那么材料的循環(huán)穩(wěn)定性和倍率性能優(yōu)于共沉淀合成的材料。為了進(jìn)一步提高材料的電化學(xué)性能,采用Mg2+和PO43-對(duì)溶膠凝膠法制備材料進(jìn)行摻雜改性,Mg2+最佳比例為x=0.01,在0.2C下循環(huán)100周材料的容量保持率高達(dá)64.9%,在1.0C下循環(huán)100周材料的放電比容量為139.4mAh/g,保持率高達(dá)97.0%;PO43-最佳比例為x=0.02,在倍率性能測試中2.0C下放電比容量仍有105.2mAh/g,容量保持率高達(dá)52.1%;這是因?yàn)殡x子摻雜摻雜增大了空間位阻,減少了離子混排和循環(huán)過程中的相變,保持了晶體結(jié)構(gòu)的穩(wěn)定性,摻雜后的材料團(tuán)聚嚴(yán)重,分散性很差,Li+脫嵌距離變長,使倍率性能下降;并采用石墨烯包覆最佳比例為3%,在0.2C下循環(huán)100周材料放電比容量為143.7mAh/g,容量保持率高達(dá)80.8%,在1.0C下循環(huán)100周材料的容量保持率高達(dá)91.8%。石墨烯不僅可以減少電解液對(duì)活性材料的腐蝕,使材料的循環(huán)穩(wěn)定性提高,而且其超高的離子和電子導(dǎo)電率,使材料的倍率性也得到改善。最后,采用溶膠凝膠法,以聚乙烯吡咯烷酮(PVP)為絡(luò)合劑,制備納米材料Li1.2Mn0.54Ni0.13Co0.13O2,粒徑約為100nm,對(duì)絡(luò)合劑PVP加入量進(jìn)行了探索和優(yōu)化。PVP最佳用量為PVP:M=1.0(M為金屬離子總量),材料在0.2C下循環(huán)100周材料的放電比容量為137.1mAh/g,容量保持率分別為68.6%,在1.0C下循環(huán)100周材料的放電比容量為125.5mAh/g,容量保持率分別為82.8%。此條件下材料具有較優(yōu)異的循環(huán)穩(wěn)定性和倍率性能,這是由于納米材料的脫嵌路徑較短,載流子脫嵌加快,大電流放電性能得到改善,同時(shí)納米材料具有更大的比表面,離子脫嵌位點(diǎn)增多,活性物質(zhì)得到有效利用,放電容量高。
[Abstract]:The lithium ion battery rich lithium manganese based cathode material xLi2MnO3 (1-x) LiMO2 has the advantages of high specific energy, long cycle life, good safety performance and so on, making it one of the ideal positive material for power batteries. In this paper, the layer rich lithium manganese based cathode material Li1.2Mn0.54Ni0.13Co0.13O2 was used as the research object, and the co precipitation (CP) and the sol-gel method (S) were used respectively. G) the target material was prepared. The crystal structure, physical morphology and electrochemical properties of the material were studied by means of XRD, SEM, CV, EIS and constant current charge discharge test. First, the precipitation pH value, the choice of lithium source, the calcining time and the calcining temperature in the co precipitation process were explored and optimized, and the best process was as follows: B Acid salt is used as the raw material, NaOH and NH4? H2O as precipitant, the precursor of hydroxide is obtained under the condition of pH=11.0. LiOH? H2O is added to the precursor of the hydroxide, and LiOH H2O is added to the lithium source. The target material is obtained by sintering 5h at 500 C and sintering 12h in air atmosphere at 900 C. The initial discharge specific capacity (0.5C, 1C=300mA/g) is 283.1mAh/g, and the efficiency of Kulun is as high as 80.7%. In 0.2C The discharge specific capacity of the lower cycle 50 weeks is 179.5mAh/g, the capacity retention rate is 76.7%. The discharge specific capacity of the material under the 1.0C cycle is 118.9mAh/g and the capacity retention rate is 73.3%. The discharge specific capacity of the material under 2.0C is still 108.2mAh/g. in order to improve the cyclic stability and multiplying performance of the material. MoO3 and Al2O3 are applied to the materials respectively. The optimum proportion of the coated modified.MoO3 coating is 1%, the first discharge specific capacity (0.5C) is 256.7mAh/g, the efficiency of Kulun is up to 83.4%. The discharge specific capacity of the material under 1.0C cycle is 107.3mAh/g, the capacity retention rate is 78.4%, the optimum proportion of the Al2O3 coating is 5%, and the capacity retention rate of the material under the 1.0C cycle is as high as 87.8%.. The coating reduces the corrosion of the electrolyte to the active material and improves the cycle stability. The conclusion is that the optimum charging cut-off voltage is 4.6V, which can reduce the decomposition of the electrolyte and inhibit the corrosion of the active material, and charge the constant current pressure of the battery to the current attenuation. To the original 1/20 is the best charging cut-off current. Secondly, the sol-gel method is used to prepare the material Li1.2Mn0.54Ni0.13Co0.13O2. The best process is: acetic acid salt as the raw material, glycolic acid as the complexing agent (glycolic acid: metal ion =1.0), pH in 7.0~8.0 by ammonia water, 5h at 450 degrees C, and sintered 12h in air atmosphere at 900 C to get the target material L The first discharge specific capacity (0.5C) of i1.2Mn0.54Ni0.13Co0.13O2. material is 275.9mAh/g, the efficiency of Kulun is as high as 74%. The discharge specific capacity of the material under 0.2C cycle is 81.3mAh/g and the capacity retention rate is 39.4%. The materials synthesized by the sol-gel method have better layer structure and good dispersibility of the material, and the active material is fully utilized. In addition, the material dispersion is good, the surface area is larger, Li+ can be rapidly deembedded. Then the cyclic stability and multiplying performance of the materials are better than the coprecipitation materials. In order to further improve the electrochemical performance of the materials, Mg2+ and PO43- are used to make the materials mixed with the sol-gel method, the optimum proportion of Mg2+ is x=0.01, and the cycle is 10 under 0.2C. The capacity retention of materials at 0 weeks is up to 64.9%. The discharge specific capacity of the material under 1.0C cycle is 139.4mAh/g, the retention rate is up to 97%, and the optimum proportion of PO43- is x=0.02. The discharge specific capacity of PO43- is still 105.2mAh/g and the capacity retention rate is up to 52.1% in the multiplex performance test. This is because ion doping increases the space resistance and decreases. The phase transformation in the process of ion mixing and circulation keeps the stability of the crystal structure. The material reunion after doping is serious, the dispersion is very poor, the Li+ declines distance becomes longer, and the ratio is reduced. The optimum proportion of graphene coating is 3%, the discharge specific capacity is 143.7mAh/g for 100 weeks under the 0.2C cycle, and the capacity retention rate is up to 80.8%, in 1.0C The capacity retention of the material up to 100 weeks is up to 91.8%. graphene, which can not only reduce the corrosion of the electrolyte to the active material, improve the circulation stability of the material, but also improve the high ionic and electronic conductivity of the material. Finally, the sol-gel method is used to use polyvinylpyrrolidone (PVP) as the complexing agent. The nano material Li1.2Mn0.54Ni0.13Co0.13O2 was prepared with a particle size of about 100nm. The optimum dosage of the complexing agent PVP was explored and optimized. The optimum amount of.PVP was PVP:M=1.0 (M is the total metal ion). The discharge specific capacity of the material under 0.2C for 100 weeks was 137.1mAh/g, the capacity retention rate was 68.6%, and the discharge ratio of the material under 1.0C under the 1.0C cycle was 100 weeks. The capacity of the material is 125.5mAh/g and the capacity retention rate is 82.8%.. The material has excellent cyclic stability and multiplying performance. This is due to the short inlay path of the nanomaterials, the acceleration of the carrier removal and the improvement of the discharge performance of the large current. At the same time, the nanomaterials have a larger specific surface, the increase of the ion embed site and the active substance. It is effectively used and the discharge capacity is high.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TM912

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