富锂三元正极材料Li-Ni-Mn-Al-O的改性研究与形貌调控
发布时间：2018-11-10 11:48
【摘要】：锂离子电池由于其高能量密度已被广泛使用作为电子产品,电动车以及混合动力车的储能装置。富锂三元层状正极材料Li-Co-Ni-Mn-O具有较高的放电比容量和热力学稳定性,然而Co的价格,毒害问题等一定程度上会限制该种材料的实际应用。与其他的有害且价格昂贵的金属元素不同,Al是一种环境友好且廉价的元素,Al的掺杂可以在NCM的表面形成Li+传输的通道,这将有益于锂离子的扩散。此外,Al的存在提升了材料中Mn3+的比率,这增大了材料的电子传输能力。同时,Al的存在可以降低材料的放电活化能并且延缓材料SEI膜的生成速率。此外,Al替代Co可以提升材料的循环性能和材料的热稳定性。因而Al替换Co制备的Li-Ni-Mn-Al-O富锂正极材料的性能是值得期待的。本试验采用溶胶凝胶法对Li-Ni-Mn-Al-O正极材料进行了比例优化,Li1.2Ni0.3Mn0.6Al0.1O2.2材料的性能最优。在优化过程中发现,Li含量低于最优化值时材料中存在尖晶石相,随着Li含量提升尖晶石相含量逐渐降低。材料达到最优Li含量后,进一步富锂,多余的Li会形成Li2O而使材料团聚,从而导致材料的性能下降。当材料中的Mn主要以四价态形式存在时,材料的性能最优。这为其他研究者设计材料提供了一个依据。为了提升材料的倍率性能和循环稳定性,分别对材料进行Fe替代Ni和Cu O包覆处理。Fe替代Ni直接降低了材料中的Ni含量,达到降低材料阳离子混排程度的目的,提升了材料的倍率性能。但过多的Fe替代会降低材料的放电比容量。对材料进行少量的Cu O包覆可以改善材料的循环稳定性,并且提升材料的倍率性能,但会牺牲材料的放电比容量。对材料的形貌进行调控,是一种有效的提升材料性能的方法。分别采用静电纺丝法,水热法和固相法制备不同形貌的材料。采用静电纺丝法可以制备扁丝状前驱体,但高温会对丝状结构造成破坏。采用水热法可以制备出片层堆叠结构的材料。此材料的循环稳定性和倍率性能要明显优于溶胶凝胶材料,30次循环之后材料的放电比容量为199.86m Ah/g,在1000m A/g充放电电流密度下,放电比容量可以达到101.35m Ah/g。采用固相法可以得到球壳结构的材料。但由于固相法制备材料的不均匀性材料的性能较差。对水热法得到的材料的工艺进行进一步的优化,优化条件包括聚乙烯吡咯烷酮(PVP)用量,进样速率和煅烧温度。发现随着PVP使用量的增加,材料由层状堆叠的结构逐渐变为单个小颗粒结构。随着进样速率的增加,材料也是由层状堆叠的结构逐渐变为单个小颗粒结构。测试发现小颗粒的材料富锂化程度很低。提升材料的烧结温度,发现材料的晶型逐渐向大块晶体结构转变,降低了材料的性能。最优化的工艺条件为,2gPVP用量,10ml/h的进样速率,750℃的煅烧温度。将水热法优化后的层状堆叠材料(HT-NMA)与溶胶凝胶材料制备的片状材料(SG-NMA)进行比较。HT-NMA材料之间接触更加充分。采用BET模型对数据进行拟合,HT-NMA的比表面积为8.92m2/g而SG-NMA的比表面积为5.90m2/g,大的比表面积使得HT-NMA与导电剂混合更加充分,会具有更好的电子传导能力。在20m A/g的电流密度下循环30圈,HT-NMA的容量保持率为86%,在1000m A/g的电流密度下HT-NMA的放电比容量为108m Ah/g。通过将Nyquist图和Bode图协同分析,发现相比于SG-NMA,HT-NMA具有更小的电子传递电阻,并且5次循环后,其高频弧增长的幅度更小。对于这两种材料,相比于SEI电阻,材料的电子传递电阻对材料的电化学性能具有更大的影响。循环前后良好的电子传递电阻是层状堆叠材料性能优异的原因。
[Abstract]:As a result of its high energy density, the lithium ion battery has been widely used as an energy storage device for electronic products, electric vehicles and hybrid vehicles. Li-Co-Ni-Mn-O with Li-Co-Ni-Mn-O has high discharge specific capacity and thermodynamic stability. However, the price of Co, the problem of poisoning and so on will limit the practical application of the material. Unlike other harmful and expensive metal elements, Al is an environment-friendly and inexpensive element, and the doping of Al can form a Li + transmission channel on the surface of the NCM, which will benefit the diffusion of lithium ions. In addition, the presence of Al increases the ratio of Mn3 + in the material, which increases the electron transport capacity of the material. At the same time, the presence of Al can reduce the discharge activation energy of the material and delay the generation rate of the material SEI film. In addition, the Al substitution Co can improve the cycle performance of the material and the thermal stability of the material. Therefore, the performance of the Li-Ni-Mn-Al-O-rich anode material prepared by the Al replacement Co is expected. The performance of Li-Ni-Mn-Al-O cathode material was optimized by sol-gel method, and Li1. 2Ni0. 3Mn0. 6Al0. 1O2. In the optimization process, the spinel phase is present in the material when the Li content is lower than the optimum value, and the content of the spinel phase increases with the content of Li. After the material has reached the optimum Li content, the lithium is further enriched, and the excess Li forms Li2O and the material is agglomerated, resulting in a decrease in the performance of the material. When the Mn in the material is mainly in the form of a tetravalent state, the performance of the material is optimal. This provides a basis for other investigator design materials. In order to improve the rate and cycle stability of the material, Fe was used to replace Ni and Cu O. and the Fe substitution Ni directly reduces the Ni content in the material, so that the purpose of reducing the cation mixing degree of the material is achieved, and the rate performance of the material is improved. However, excessive Fe substitution can reduce the discharge specific capacity of the material. a small amount of cu o-coating of the material can improve the cycle stability of the material and increase the rate performance of the material, but the discharge specific capacity of the material is sacrificed. The method for controlling the morphology of the material is an effective method for improving the performance of the material. The materials of different shapes were prepared by electrostatic spinning, hydrothermal method and solid phase method, respectively. The flat-filament precursor can be prepared by the electrospinning method, but the high temperature can cause damage to the filamentous structure. the material of the sheet stacking structure can be prepared by adopting a water thermal method. The cycle stability and the rate performance of this material are obviously superior to that of the sol-gel material. The discharge specific capacity of the material after 30 cycles is 1996.86m Ah/ g, and the discharge specific capacity can reach 101.35m Ah/ g at the charge-discharge current density of 1000m A/ g. and the material of the spherical shell structure can be obtained by adopting a solid-phase method. but the performance of the non-uniform material of the material is poor due to the solid phase method. The process of the material obtained by the hydrothermal method is further optimized, and the optimization conditions include the amount of the polynorbornene (PVP), the sample rate and the burn-in temperature. it has been found that as the amount of pvp is increased, the material gradually becomes a single small particle structure from the structure of the layered stack. As the sample rate increases, the material is also gradually changed from the structure of the layered stack to a single small particle structure. the test found that the material with the small particles had a low level of lithium-rich. the sintering temperature of the material is increased, and the crystal type of the material is found to gradually change to the bulk crystal structure, and the property of the material is reduced. The optimized process conditions were, for example, an amount of 2gPVP, a sample rate of 10 ml/ h, a burn-in temperature of 750. degree. C. The layered stack material (HT-NMA), which was optimized by hydrothermal method, was compared to a sheet material (SG-NMA) made of a sol-gel material. the contact between the ht-nma materials is more sufficient. The specific surface area of the HT-NMA is 8.9m2/ g and the specific surface area of the SG-NMA is 5.90m2/ g, and the specific surface area of the HT-NMA is 5.90m2/ g. The capacity retention of HT-NMA was 86% at the current density of 20 m A/ g, and the discharge specific capacity of HT-NMA at the current density of 1000m A/ g was 108m Ah/ g. It is found that HT-NMA has a smaller electron transfer resistance than SG-NMA and HT-NMA, and the increase of high-frequency arc is smaller after 5 cycles. For both materials, the electron transfer resistance of the material has a greater effect on the electrochemical performance of the material compared to the SEI resistance. The good electron transfer resistance before and after the cycle is the cause of the excellent performance of the layered stacked material.
【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】：2017
【分类号】：TM912
[Abstract]:As a result of its high energy density, the lithium ion battery has been widely used as an energy storage device for electronic products, electric vehicles and hybrid vehicles. Li-Co-Ni-Mn-O with Li-Co-Ni-Mn-O has high discharge specific capacity and thermodynamic stability. However, the price of Co, the problem of poisoning and so on will limit the practical application of the material. Unlike other harmful and expensive metal elements, Al is an environment-friendly and inexpensive element, and the doping of Al can form a Li + transmission channel on the surface of the NCM, which will benefit the diffusion of lithium ions. In addition, the presence of Al increases the ratio of Mn3 + in the material, which increases the electron transport capacity of the material. At the same time, the presence of Al can reduce the discharge activation energy of the material and delay the generation rate of the material SEI film. In addition, the Al substitution Co can improve the cycle performance of the material and the thermal stability of the material. Therefore, the performance of the Li-Ni-Mn-Al-O-rich anode material prepared by the Al replacement Co is expected. The performance of Li-Ni-Mn-Al-O cathode material was optimized by sol-gel method, and Li1. 2Ni0. 3Mn0. 6Al0. 1O2. In the optimization process, the spinel phase is present in the material when the Li content is lower than the optimum value, and the content of the spinel phase increases with the content of Li. After the material has reached the optimum Li content, the lithium is further enriched, and the excess Li forms Li2O and the material is agglomerated, resulting in a decrease in the performance of the material. When the Mn in the material is mainly in the form of a tetravalent state, the performance of the material is optimal. This provides a basis for other investigator design materials. In order to improve the rate and cycle stability of the material, Fe was used to replace Ni and Cu O. and the Fe substitution Ni directly reduces the Ni content in the material, so that the purpose of reducing the cation mixing degree of the material is achieved, and the rate performance of the material is improved. However, excessive Fe substitution can reduce the discharge specific capacity of the material. a small amount of cu o-coating of the material can improve the cycle stability of the material and increase the rate performance of the material, but the discharge specific capacity of the material is sacrificed. The method for controlling the morphology of the material is an effective method for improving the performance of the material. The materials of different shapes were prepared by electrostatic spinning, hydrothermal method and solid phase method, respectively. The flat-filament precursor can be prepared by the electrospinning method, but the high temperature can cause damage to the filamentous structure. the material of the sheet stacking structure can be prepared by adopting a water thermal method. The cycle stability and the rate performance of this material are obviously superior to that of the sol-gel material. The discharge specific capacity of the material after 30 cycles is 1996.86m Ah/ g, and the discharge specific capacity can reach 101.35m Ah/ g at the charge-discharge current density of 1000m A/ g. and the material of the spherical shell structure can be obtained by adopting a solid-phase method. but the performance of the non-uniform material of the material is poor due to the solid phase method. The process of the material obtained by the hydrothermal method is further optimized, and the optimization conditions include the amount of the polynorbornene (PVP), the sample rate and the burn-in temperature. it has been found that as the amount of pvp is increased, the material gradually becomes a single small particle structure from the structure of the layered stack. As the sample rate increases, the material is also gradually changed from the structure of the layered stack to a single small particle structure. the test found that the material with the small particles had a low level of lithium-rich. the sintering temperature of the material is increased, and the crystal type of the material is found to gradually change to the bulk crystal structure, and the property of the material is reduced. The optimized process conditions were, for example, an amount of 2gPVP, a sample rate of 10 ml/ h, a burn-in temperature of 750. degree. C. The layered stack material (HT-NMA), which was optimized by hydrothermal method, was compared to a sheet material (SG-NMA) made of a sol-gel material. the contact between the ht-nma materials is more sufficient. The specific surface area of the HT-NMA is 8.9m2/ g and the specific surface area of the SG-NMA is 5.90m2/ g, and the specific surface area of the HT-NMA is 5.90m2/ g. The capacity retention of HT-NMA was 86% at the current density of 20 m A/ g, and the discharge specific capacity of HT-NMA at the current density of 1000m A/ g was 108m Ah/ g. It is found that HT-NMA has a smaller electron transfer resistance than SG-NMA and HT-NMA, and the increase of high-frequency arc is smaller after 5 cycles. For both materials, the electron transfer resistance of the material has a greater effect on the electrochemical performance of the material compared to the SEI resistance. The good electron transfer resistance before and after the cycle is the cause of the excellent performance of the layered stacked material.
【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】：2017
【分类号】：TM912
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