基于沸石咪唑酯骨架-8的LiFePO_4改性

商业化LiFePO_4(LFP)正极材料的导电性一直是制约其性能提高的关键。为了提高LFP的性能,利用沸石咪唑酯骨架-8(ZIF-8)制备多孔碳材料(CZIF-8)改善商业化LFP正极材料的导电性,对比了两种改性LFP的方法:1)将退火的ZIF-8以物理混合的方法与LFP混合制得LFP/CZIF-8正极材料;2)ZIF-8在LFP表面原位生长后退火制得LFP@CZIF-8正极材料。X射线粉末衍射(XRD)、氮气吸脱附(BET)和拉曼光谱等测试证明,改性后的LFP仍具有橄榄石型结构,同时出现了具有介孔结构的石墨化碳材料的特征。扫描电子显微镜(SEM)和透射电子显微镜(TEM)测试证明LFP/CZIF-8样品中LFP与CZIF-8之间未形成链接结构,而在LFP@CZIF-8样品中二者形成了核壳结构。电化学阻抗测试(EIS)表明,改性后样品的离子传输阻抗明显减小,说明两种方法均提高了LFP的导电性。充放电循环测试表明,两种改性方法均能提高LFP的循环性能和库伦效率。不同的是,倍率性能测试表明,LFP/CZIF-8样品的高倍率性能比LFP@CZIF-8样品更有优势,在10.0 C电流倍率下能够达到57.8 m A·h/g。这一研究为商业化锂离子电池电极材料的改性提供了新的思路,并且通过方法优化为产业化做了铺垫。

Modification of LiFePO4 Based on Zeolite Imidazolate Framework-8

The conductivity of commercial LiFePO₄(LFP) cathode materials has been the key to improving its electrochemical performance. Porous carbon was prepared by using zeolite imidazolate framework-8(ZIF-8) to improve the conductivity of commercial LFP cathode material for enhancing its electrochemical performance. Two routes for modifying LFP are compared:1)the carbonized ZIF-8(C_ZIF-8) was mixed with LFP to form LFP/C_ZIF-8 cathode material; 2)the LFP@C_ZIF-8 cathode material was obtained by in situ growth and annealing of ZIF-8 on the surface of LFP. X-ray powder diffraction(XRD), N₂ adsorption and desorption isotherms(BET) and Raman spectra reveal that the modified LFP still has an olivine structure, and the characteristics of graphite carbon materials with mesoporous structure appear at the same time. Scanning electron microscopy(SEM) and transmission electron microscopy(TEM) tests display that there is no link structure between LFP and C_ZIF-8 in the LFP/C_ZIF-8 samples, while LFP@C_ZIF-8 sample has a core-shell structure. Electrochemical impedance spectroscopy(EIS) shows that the ion transport impedance of the modified samples decreased significantly, indicating that the conductivity of LFP can be improved by these two routes. The charge-discharge cycle test proves that the two modified methods can improve the cycle performance and Coulombic efficiency of LFP cathode material. The high C rate charge-discharge test shows that the LFP/C_ZIF-8 sample is better than LFP@C_ZIF-8 sample, the discharge capacity of LFP/C_ZIF-8 sample can reach 57.8 mA·h/g at 10.0 C. This research provides a new idea for the modification of commercial lithium ion battery electrode materials, and lays the foundation for industrialization via the method optimization.