高导电性Ti_3SiC_2改性LiFePO_4/C及其电化学性能

Electrochemical Performance of LiFePO_4/C Modified with High Conducting Ti_3SiC_2

LiFePO4具有优良的综合电化学性能,然而它的高倍率性能较差。为了提高其导电性能,进而改善高倍率电化学性能,利用高导电性Ti3SiC2来改性LiFePO4。采用球磨法将Ti3SiC2与LiFePO4进行均匀混合,研究Ti3SiC2添加量对LiFePO4电化学性能的影响。当Ti3SiC2质量分数为4%时,电化学综合性能最好。1、2、5 C的放电容量分别为131.7、119.6、97.4 mAh·g 1,而不加Ti3SiC2试样在相应倍率的放电容量仅为120.8、101.9、64.0 mAh·g 1;恒电位阶跃测试表明添加4%Ti3SiC2使锂离子的扩散速率从8.5×10 11cm2·s 1提高到8.2×10 10cm2·s 1;交流阻抗和循环伏安测试还发现Ti3SiC2的加入降低了电荷转移电阻,提高了电极材料的可逆性,从而改善了充放电过程中的动力学限制,提高了高倍率下的放电容量。

Lithium iron phosphate is a new kind of cathode materials for lithium ion battery. It has found wide applications in lithium ion battery industry. It has excellent comprehensive electrochemical performance. Unfortunately, its high rate performance is not satisfactory. In order to enhance its conductivity and improve the high rate performance of the cathode material, highly conductive Ti3SiC2 modification was adopted. Ti3SiC2 modified LiFePO4/C powders were prepared via a ball milling process followed by heat-treatment at 400 ℃. The effects of addition amount of Ti3SiC2 on electrochemical performance of the cathode material were investigated. It is found that a Ti3SiC2-based conducting network characterized by a ＂plane-to-point＂ conducting mode is constituted in the LiFePO4/C cathode. Galvanostatic charge/discharge test indicates that Ti3SiC2 modification is effective to improve the discharge capacity at high rates. Cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and potential step chronoamperometry （PSCA） measurements prove that the Ti3SiC2-based conducting network enhances electrochemical reversibility, alleviates charge transfer impedance and facilitates lithium ion diffusion （from 8.5x10-11 cm2.s-1 to 8.2x10-10 cm2·s-l）. The 4wt% Ti3SiC2-modified LiFePO4 sample exhibits the best electrochemical performance with capacities of 131.7, 119.6 and 97.4 mAh.g-1 at 1 C, 2 C and 5 C, respectively, much higher than those without Ti3SiC2 modification. They are only 120.8, 101.9 and 64.0 mAh.R-1 at the corresponding rates, resnectivelv.