钛掺杂磷酸铁锂的合成及其充放电性能研究

Synthesis and charge/discharge performances of titanium doped lithium iron phosphate

  • 摘要: 元素掺杂是提高磷酸铁锂(LiFePO4)正极材料充放电性能的主要途径之一。以TiO2为钛源,采用高温固相还原法合成了Ti掺杂的LiFePO4,通过XRD、XPS、SEM和BET等技术表征了钛掺杂LiFePO4的结构组成、微观形貌和理化性能,进而对组成-结构与其充放电性能之间的影响关系进行了研究。结果表明:钛掺杂LiFePO4在0.1 C和1 C倍率下的首次放电比容量最高分别达到161.9 mAh/g和150.8 mAh/g,比未掺杂钛的LiFePO4提高4.72%和7.48%,且在1 C倍率下循环150周后容量保持率高达98.54%。这主要归因于Ti4+取代Fe2+进入LiFePO4晶格,稳固晶体结构的同时会抑制晶粒的二次生长,导致Li+脱/嵌路径减小,迁移效率加快,进而提高了LiFePO4的放电比容量、倍率以及循环性能。

     

    Abstract: Element doping is one of the main ways to improve the charge/discharge performances of lithium iron phosphate (LiFePO4) cathode materials. In this paper, modified LiFePO4 was synthesized by a high-temperature solid-state reduction method using TiO2 as a titanium source. The structural composition, micro-morphology, and physicochemical properties of titanium-doped LiFePO4 were characterized by XRD, XPS, SEM, and BET, and further, the relationship between composition-structure and charge/discharge performances was carefully studied. The results indicate that the first discharge-specific capacity of titanium doped LiFePO4 respectively reaches the maximum of 161.9 and 150.8 mAh/g at 0.1 C and 1 C rate, which is 4.72% and 7.48% higher than LiFePO4 without titanium doping, and the capacity retention rate achieves as high as 98.54% after 150 cycles at 1 C rate. This is mainly attributed to the substitution of Fe2+ by Ti4+ into LiFePO4 lattice, which stabilizes the crystal structure and inhibits the secondary growth of crystalline grains, leading to a decrease in Li+ extraction/insertion paths and an increase in migration efficiency, thereby improving the discharge specific capacity, rate, and cycle performances of LiFePO4.

     

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