锂离子电池正极材料硅酸锰锂的制备及其改性研究
发布时间:2018-10-20 13:51
【摘要】:锂离子电池正极材料Li_2MnSiO_4具有理论容量高(333.0 mAh g-1)、热稳定好、成本低以及对环境友好等特点。但是该材料也有很多缺点,如电子导电性低、在循环过程中结构坍塌以及Mn在电解液中溶解,从而导致其循环性能较差。本论文主要对Li_2MnSiO_4材料的制备以及改性进行了系统性的研究。通过XRD、SEM、EDS、TEM等方法对合成的样品进行物理表征,恒流充放电测试、循环伏安曲线以及交流阻抗法对其进行电化学表征。采用快速溶胶凝胶法合成了Li_2MnSiO_4/C材料,硅源为有机的硅酸四乙酯(TEOS)。研究了不同合成工艺对合成样品的结构和电化学性能的影响,探索出了合成Li_2MnSiO_4/C材料的最佳工艺:乙酸量为10 g,煅烧温度为650 ℃,煅烧时间为6 h,碳含量为20 wt%。但是由于Li_2MnSiO_4材料在充放电过程中结构坍塌的本质缺陷以及Mn在电解液中的溶解,在最优条件下合成的样品循环性能仍不令人满意。为了提高溶胶凝胶法合成的Li_2MnSiO_4/C材料电化学性能,我们分别对其在Mn位和Si位进行离子掺杂。在Mn位掺杂共价离子(Zn~(2+)和Cu~(2+))和异价离子(Ag~+和Cr~(3+)),Li_2MnSiO_4/C样品的电化学性能都有不同程度的提高。在硅位掺杂Al~(3+)离子可以使样品中的锂含量增加,合成的不同含量Al~(3+)离子掺杂的样品中,Li2.02MnSi0.98Al0.02O4/C样品呈现出了最优的电化学性能。首次提出氧化物和碳共包覆来提高Li_2MnSiO_4材料的性能。本论文研究了三种不同的氧化物材料MoO_2,ZnO和TiO_2对Li_2MnSiO_4/C材料的结构和性能的影响。一步溶胶凝胶法合成的不同含量MoO_2包覆的Li_2MnSiO_4/C材料中,包覆量为1wt%时,材料呈现了最优的电化学性能,在0.1 C倍率下的首次放电容量为184.9mAh g-1。包覆ZnO和TiO_2的最优样品在0.1 C倍率下的放电容量分别为182.8和186.4 mAh g-1。并且,包覆后的样品都呈现出了较好的循环性能。通过非原位XRD分析可知,包覆氧化物可以在一定程度上抑制结构的坍塌。ICP测试表明,氧化物可以减少Mn在循环过程中溶于电解液中的浓度。首次采用水热法,使用无机的硅酸代替有机的TEOS作为硅源来合成Li_2MnSiO_4/C材料。考察了不同的合成条件对最终样品结构和电化学性能的影响。得到该方法制备Li_2MnSiO_4/C材料的最优条件为:水热反应温度为180 ℃,水热反应时间为36 h,煅烧温度为600 ℃,溶剂中添加20 ml的乙二醇,煅烧时间为10 h。最优样品在0.1 C和0.5 C倍率下的首次放电比容量分别为171.7和159.4 mAh g-1。
[Abstract]:Lithium ion battery cathode material Li_2MnSiO_4 has the advantages of high theoretical capacity (333.0 mAh g ~ (-1), good thermal stability, low cost and environmental friendliness. However, the material also has many disadvantages, such as low electrical conductivity, structure collapse during cycling and dissolution of Mn in electrolyte, which results in poor cycling performance. In this paper, the preparation and modification of Li_2MnSiO_4 materials were studied systematically. The samples were characterized by XRD,SEM,EDS,TEM, constant current charge-discharge test, cyclic voltammetry and AC impedance method. Li_2MnSiO_4/C materials were synthesized by a rapid sol-gel method with organic tetraethyl silicate (TEOS). As the source. The effects of different synthetic processes on the structure and electrochemical properties of the synthesized Li_2MnSiO_4/C materials were studied. The optimum conditions for the synthesis of Li_2MnSiO_4/C materials were found: the amount of acetic acid was 10 g, the calcination temperature was 650 鈩,
本文编号:2283367
[Abstract]:Lithium ion battery cathode material Li_2MnSiO_4 has the advantages of high theoretical capacity (333.0 mAh g ~ (-1), good thermal stability, low cost and environmental friendliness. However, the material also has many disadvantages, such as low electrical conductivity, structure collapse during cycling and dissolution of Mn in electrolyte, which results in poor cycling performance. In this paper, the preparation and modification of Li_2MnSiO_4 materials were studied systematically. The samples were characterized by XRD,SEM,EDS,TEM, constant current charge-discharge test, cyclic voltammetry and AC impedance method. Li_2MnSiO_4/C materials were synthesized by a rapid sol-gel method with organic tetraethyl silicate (TEOS). As the source. The effects of different synthetic processes on the structure and electrochemical properties of the synthesized Li_2MnSiO_4/C materials were studied. The optimum conditions for the synthesis of Li_2MnSiO_4/C materials were found: the amount of acetic acid was 10 g, the calcination temperature was 650 鈩,
本文编号:2283367
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