富锂锰基三元正极材料的制备与改性研究

发布时间：2018-06-20 19:30

本文选题：锂离子电池 + 富锂材料　；参考：《哈尔滨工业大学》2016年硕士论文

【摘要】：锂离子电池富锂锰基正极材料xLi2MnO3·(1-x)LiMO2具有比能量高、循环寿命长、安全性能好等优点,使其成为动力电池的理想正极材料之一。本文以层状富锂锰基正极材料Li1.2Mn0.54Ni0.13Co0.13O2为研究对象,分别采用共沉淀法(CP)和溶胶凝胶法(SG)制备出目标材料,通过XRD、SEM、CV、EIS和恒流充放电测试等手段,深入研究了材料的晶体结构、物理形貌和电化学性能。首先,对共沉淀法制备工艺中的沉淀pH值,锂源的选择,煅烧时间以及煅烧温度进行了探索和优化,得出最佳工艺为:以乙酸盐为原料,NaOH和NH4?H2O为沉淀剂,在pH=11.0条件下得到氢氧化物前驱体,在氢氧化物前驱体中加入LiOH?H2O为锂源,500℃预烧5h,900℃空气气氛中烧结12h得到目标材料。材料的首次放电比容量(0.5C,1C=300mA/g)为283.1mAh/g,库伦效率高达80.7%,在0.2C下循环50周材料的放电比容量为179.5mAh/g,容量保持率为76.7%,在1.0C下循环100周材料的放电比容量为118.9mAh/g,容量保持率为73.3%,2.0C下材料的放电比容量仍有为108.2mAh/g。为了改善材料的循环稳定性和倍率性能,采用MoO3和Al2O3对材料分别进行包覆改性。MoO3包覆最佳比例为1%,此材料的首次放电比容量(0.5C)为256.7mAh/g,库伦效率高达83.4%,在1.0C下循环100周材料的放电比容量为107.3mAh/g,容量保持率分别为78.4%;Al2O3包覆最佳比例为5%,在1.0C下循环100周材料的容量保持率高达87.8%。包覆层减少了电解液对活性材料的腐蚀,循环稳定性提高。对共沉淀法制备的材料进行充放电机制的探究,得出结论为:最佳充电截止电压为4.6V,此电压下可以减少电解液的分解,抑制对活性材料的腐蚀,而将电池恒流恒压充至电流衰减至原来的1/20为最佳充电截止电流。其次,采用溶胶凝胶法制备材料Li1.2Mn0.54Ni0.13Co0.13O2,最佳工艺为:以乙酸盐为原料,乙醇酸为络合剂(乙醇酸:金属离子=1.0),采用氨水调节pH在7.0~8.0之间,450℃预烧5h,900℃空气气氛中烧结12h得到目标材料Li1.2Mn0.54Ni0.13Co0.13O2。材料的首次放电比容量(0.5C)为275.9mAh/g,库伦效率高达74.0%,在0.2C下循环100周材料的放电比容量为81.3mAh/g,容量保持率为39.4%,溶胶凝胶法合成的材料具有较好的层状结构以及材料的分散性好,活性物质得以充分利用,且材料分散性较好,比表面积大,Li+可实现快速脱嵌,那么材料的循环稳定性和倍率性能优于共沉淀合成的材料。为了进一步提高材料的电化学性能,采用Mg2+和PO43-对溶胶凝胶法制备材料进行掺杂改性,Mg2+最佳比例为x=0.01,在0.2C下循环100周材料的容量保持率高达64.9%,在1.0C下循环100周材料的放电比容量为139.4mAh/g,保持率高达97.0%;PO43-最佳比例为x=0.02,在倍率性能测试中2.0C下放电比容量仍有105.2mAh/g,容量保持率高达52.1%;这是因为离子掺杂掺杂增大了空间位阻,减少了离子混排和循环过程中的相变,保持了晶体结构的稳定性,掺杂后的材料团聚严重,分散性很差,Li+脱嵌距离变长,使倍率性能下降;并采用石墨烯包覆最佳比例为3%,在0.2C下循环100周材料放电比容量为143.7mAh/g,容量保持率高达80.8%,在1.0C下循环100周材料的容量保持率高达91.8%。石墨烯不仅可以减少电解液对活性材料的腐蚀,使材料的循环稳定性提高,而且其超高的离子和电子导电率,使材料的倍率性也得到改善。最后,采用溶胶凝胶法,以聚乙烯吡咯烷酮(PVP)为络合剂,制备纳米材料Li1.2Mn0.54Ni0.13Co0.13O2,粒径约为100nm,对络合剂PVP加入量进行了探索和优化。PVP最佳用量为PVP:M=1.0(M为金属离子总量),材料在0.2C下循环100周材料的放电比容量为137.1mAh/g,容量保持率分别为68.6%,在1.0C下循环100周材料的放电比容量为125.5mAh/g,容量保持率分别为82.8%。此条件下材料具有较优异的循环稳定性和倍率性能,这是由于纳米材料的脱嵌路径较短,载流子脱嵌加快,大电流放电性能得到改善,同时纳米材料具有更大的比表面,离子脱嵌位点增多,活性物质得到有效利用,放电容量高。
[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.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM912

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