碳热还原法制备磷酸铁锂及其改性研究

发布时间：2018-01-10 23:08

  本文关键词：碳热还原法制备磷酸铁锂及其改性研究　出处：《长沙理工大学》2014年硕士论文　论文类型：学位论文

  更多相关文章： 磷酸铁 磷酸铁锂 碳热还原法 阳离子掺杂

【摘要】：碳热还原法(CTR)由高温固相法衍生而来,且其操作简单,以三价铁为铁源其产物更为均匀而且不需要采用FeC204.H2O因而价格便宜。用于CTR法的铁源有很多,如Fe(OH)3、Fe2O3、Fe3O4、FePO4以及复合铁源等。其中,FePO4既能够提供铁源也能够提供磷源,且在FePO4转变成LiFePO4的过程中二者的结构相似。因此,通过控制FePO4的粒径和形貌有望实现对LiFePO4的粒径和形貌的有效调控。本文先通过沉淀法制得FePO4,再以其为原料合成LiFePO4,优化了CTR法合成LiFePO4的条件并系统地研究了FePO4制备的条件对其结构和形貌的影响以及对后续制备的LiFePO4的影响。用XRD、ICP、SEM和TEM表征FePO4和LiFePO4的组成、结构以及形貌,研究其构效规律。采用蓝电、电化学工作站对LiFePO4的充放电特性及其交流阻抗和循环伏安特性进行测定,研究锂离子脱嵌动力学。沉淀法制备FePO4。研究了在该方法中反应物、水浴温度、pH值、浓度、搅拌速度以及添加剂对制备的FePO4粒度、形貌和结晶性的影响。研究表明：采用FeSO4·7H2O-NH4H2PO4为反应物有助于类球形的磷酸铁的形成。在该体系中,温度为90℃、pH为1.7左右、搅拌速度采用400r/min、表面活性剂为SDS时能够得到粒径为20-80nm且结晶良好、分散均匀的FePO4粉末。CTR法合成LiFePO4。选取Li2CO3、C6H12O6以及FePO4为原料,分别研究了烧结工艺、锂铁比、碳用量、分散介质以及前驱体的工艺条件对CTR法制备LiFePO4的影响。研究表明：在Li:Fe为1.02,19wt%的葡萄糖用量,水做分散剂,750℃下烧结12h制备的LiFePO4的首次可逆容量最高,大倍率性能最优,同时极化小,循环性能好。该样品在0.1、0.2和0.5C下的首次放电比容量依次为151、150和144mAh/g。阳离子掺杂改性LiFePO4。首先选取了镁、钒以及镍作为掺杂物对最终制备的磷酸铁锂的影响进行了探讨。其中,选用V2Os为掺杂剂能够最有效的实现对LiFePO4的放电比容量以及稳定性的优化。结果表明V的用量为3%的样品的电’化学性能最优,0.1C下的首次可逆容量为151 mAh/g,并且循环100次后没有明显的降低。
[Abstract]:Carbothermal reduction method (CTR) is derived from high temperature solid state method and its operation is simple. Taking trivalent iron as Tie Yuan's product is more uniform and it is cheaper to use FeC204.H2O. For example, there are a lot of Tie Yuan used in CTR method, such as FeOHZ3Fe2O3. Fe3O4FePO4 and compound Tie Yuan, among them, FePO4 can not only provide Tie Yuan but also provide phosphorus source. And in the process of FePO4 to LiFePO4, the structure of the two is similar. By controlling the particle size and morphology of FePO4, it is expected to achieve the effective control of the particle size and morphology of LiFePO4. Firstly, FePO4 was prepared by precipitation method. Then LiFePO4 was synthesized by using it as raw material. The conditions for the synthesis of LiFePO4 by CTR method were optimized, and the effects of the conditions of FePO4 preparation on the structure and morphology of FePO4 and on the subsequent LiFePO4 preparation were studied systematically. XRD was used. The composition, structure and morphology of FePO4 and LiFePO4 were characterized by ICP-SEM and TEM. The charge-discharge characteristics, AC impedance and cyclic voltammetry of LiFePO4 were measured by electrochemical workstation. The kinetics of lithium ion deintercalation was studied. FePO _ 4 was prepared by precipitation method. In this method, the reactants, water bath temperature, pH value, concentration, stirring speed and the particle size of FePO4 prepared by additives were studied. The effect of morphology and crystallinity. The results show that FeSO4 路7H _ 2O -NH _ 4H _ 2PO _ 4 is used as reactant to facilitate the formation of spheroidal ferric phosphate. In this system, the temperature is 90 鈩，

本文编号：1407146