单分散球形磷酸铁锂粉体的制备

发布时间：2018-06-15 22:17

  本文选题：磷酸铁锂 + 单分散　； 参考：《兰州大学》2014年硕士论文

【摘要】：锂离子电池是新一代的绿色电源,它具有比能量大、工作电压高、工作温度范围宽、循环寿命长、无记忆效应、自放电小等优点,已被广泛应用于多种便携式电子产品的移动电源以及电动车和混合动力电动车等的电源。 锂离子电池中,其正极材料对锂离子蓄电池性能起到了关键性的作用。传统的锂离子蓄电池的正极材料主要集中在锂的过渡金属氧化物如LiMO2Ni、Mn)和LiMn2O4。但LiCoO2成本较高、毒性较大、耐过充性差、资源贫乏；LiNiO2热稳定性差、制备比较困难；LiMn2O4虽然资源丰富、对环境无毒、价格便宜,但其容量较低,高温稳定性能和循环稳定性能较差。因此,研发新型的锂离子正极材料成为目前的重点和热点。 自从Padhi的研究小组在1997年提出锂离子电池的正极材料磷酸铁锂以来,具有橄榄石结构的LiFePO4材料作为锂离子电池的正极材料,由于其具有低的成本、毒性小、原材料来源比较丰富和适应高温工作环境等优点而成为目前的研究热点之一。但是,LiFePO4在实际的应用中还存在下列不足：第一,较低的电子传导率(10-7～10-9S·cm-1),这导致在锂离子电池的充放电过程中,电子不能及时的转移,产生了较大容抗,从而影响了磷酸铁锂的电化学性能；第二,较小的Li+扩散速率(1.8×10-16～2.2×10-14cm2·s-1),这导致在锂离子电池的充放电过程中,锂离子脱嵌滞后,从而降低了磷酸铁锂的容量性能和倍率性能；第三,较低的振实密度(一般商用1.0g·cm-3左右),导致磷酸铁锂体积比能量较低。 可以使用三种方法去解决上述问题。第一,通过包覆导电层(碳、纳米铜和纳米银)和金属离子掺杂(Ni+)来提高电子导电率锂离子扩散速率。第二,通过调节合成参数来减小颗粒尺寸,这样可以缩短锂离子的扩散距离,进而提高扩散速率。第三,通过制备球形的颗粒来提高振实密度。 本硕士论文主要包括下面三个方面的内容： (1)使用分析纯的FeSO4·7H2O, H3PO4和LiOH·H2O为原料,柠檬酸为络合剂,通过水热合成法制备了具有孔隙结构的单分散微米球形磷酸铁锂。在制备过程中,柠檬酸的加入起到非常关键的作用；研究了铁离子的浓度,反应温度,反应时间,柠檬酸和磷酸用量对磷酸铁锂颗粒形貌的影响,通过调节以上参数最终成功制备了由片状纳米颗粒堆积而成的微米尺度单分散球形磷酸铁锂颗粒,扫描电子显微镜的结果表明：微米球的平均粒径尺寸是18μm,而构成球形结构的片状颗粒的厚度是50nm；这种球形颗粒具有较高的比表面积(15.3m2g-1),因此,增大了颗粒与电解液的接触面积,从而大幅度的提高材料的电化学性能；这种合成方法为其他由片状颗粒堆积而成的球形颗粒的制备提供了新的方向。 (2)Ni+掺杂量(LiFe1-xNixPO4,x=0.075,0.100,0.125,0.150,0.175)对(1)中制备的LiFePO4球形颗粒形貌的影响。Ni+的掺杂量影响了球形颗粒的形貌和组成球形颗粒的纳米片的疏密程度。当x=0.075,0.100时,保持了球形颗粒的形貌；当x=0.125,0.150时,颗粒形貌呈现类球形；当x=0.175时,大部分球形颗粒的形貌被破坏。 (3)采用溶胶-凝胶法,通过Fe(NO3)3-9H2O和H3PO4混合溶液陈化制备得到单分散球形纳米FePO4-2H2O粉体。发现随着FeNO3-9H2O浓度的增大,制得样品的颗粒尺寸有变小的趋势,分散性没有明显的变化：随着保温时间的延长,制得样品的颗粒尺寸有没有明显的变化,分散性和均一性变好；以FePO4-2H2O为前驱体(?)LiOH·H2O混合在650℃氩气(95%)和氢气(5%)保护下煅烧12h合成了纳米单分散球形LiFePO4粉体。
[Abstract]:The lithium ion battery is a new generation of green power supply , which has the advantages of large specific energy , high working voltage , wide working temperature range , long cycle life , no memory effect , small self - discharge , and the like , and has been widely applied to the mobile power supply of various portable electronic products and the power supply of electric vehicles and hybrid electric vehicles .

The positive electrode material of the lithium ion battery plays a key role in the performance of the lithium ion battery . The positive electrode material of the traditional lithium ion battery is mainly concentrated in the transition metal oxide ( such as LiMO2Ni , Mn ) and limn4 , but the cost is higher , the toxicity is large , the overcharge resistance is poor , and the resource is poor ;
poor thermal stability of linioO2 and difficult preparation ;
Although the resources are abundant , the environment is non - toxic , the price is low , but the capacity is low , the high - temperature stability and the cycle stability can be poor . Therefore , the research and development of the novel lithium - ion cathode material becomes the current focus and hot spot .

Since Padhi ' s research team put forward the positive pole material lithium iron phosphate of Li - ion battery in 1997 , LiFePO4 material with olivine structure has become one of the current research hotspots due to its low cost , low toxicity , abundant raw material source and adaptability to high - temperature working environment . However , LiFePO4 also has the following disadvantages in practical application : first , lower electron conductivity ( 10 - 7 - 10 - 9S 路 cm - 1 ) , which leads to the failure of timely transfer of electrons in the charge and discharge process of lithium ion battery , thus affecting the electrochemical performance of lithium iron phosphate .
The second , smaller Li + diffusion rate ( 1.8 脳 10 - 16 ~ 2.2 脳 10 - 14 cm ~ 2 路 s - 1 ) , which leads to the lithium ion deintercalation lag during the charge and discharge of the lithium ion battery , thus reducing the capacity and rate performance of lithium iron phosphate .
Third , lower tap density ( typically around 1.0 g 路 cm - 3 ) results in a lower volume of lithium iron phosphate than energy .

First , by coating the conductive layer ( carbon , nano copper and nano silver ) and metal ion doping ( Ni + ) to improve the electron conductivity lithium ion diffusion rate . Second , by adjusting the synthesis parameters to reduce the particle size , the diffusion distance of lithium ions can be shortened , and the diffusion rate can be improved . Thirdly , the solid density can be improved by preparing spherical particles .

This Master ' s thesis mainly includes the following three aspects :

( 1 ) using analytically pure FeSO4.7H2O , H3PO4 and LiOH.H2O as raw materials , citric acid as a complexing agent , and preparing monodisperse micron spherical lithium iron phosphate with pore structure by hydrothermal synthesis .
The effects of concentration of iron ions , reaction temperature , reaction time , citric acid and phosphoric acid on the morphology of lithium iron phosphate particles were studied .
The spherical particles have higher specific surface area ( 15.3 m2g - 1 ) , therefore , the contact area between the particles and the electrolyte is increased , so that the electrochemical performance of the material is greatly improved ;
The synthetic method provides a new direction for the preparation of other spherical particles which are piled up by sheet - shaped particles .

( 2 ) The influence of Ni + doping amount ( LiFePO4 1 - xNixPO4 , x = 0.075 , 0.100 , 0.125 , 0.150 , 0.175 ) on the morphology of spherical particles of LiFePO4 prepared in ( 1 ) . The doping amount of Ni + affected the morphology of spherical particles and the density of spherical particles .
When x = 0.125 , 0.150 , the morphology of the particles is spherical ;
When x = 0.175 , the morphology of most spherical particles was destroyed .

( 3 ) By the sol - gel method , the monodisperse spherical nano FePO4 - 2H2 powder was prepared by aging of Fe ( NO3 ) 3 - 9H2O and H3PO4 . It was found that with the increase of the concentration of FeNO3 - 9H2O , the particle size of the prepared sample was smaller .
Nano monodisperse spherical LiFePO4 powder was synthesized by calcining at 650 鈩，

本文编号：2023828