由PAA-Li制L iFePO_4/C及其充放电性能与容量损失

Synthesis of LiFePO_4/C from PAA-Li and Its Charge/Discharge Performance and Capacity Loss

合成聚丙烯酸锂(PAA-L i),并以它为部分锂源及碳源,合成了磷酸亚铁锂/碳。以此为活性物质制成正电极。以PAA-L i和L iOH.H2O分别为75%和25%锂源、于625℃下灼烧24 h,所得的样品(样品号AA75625)在20℃时,第10个循环的放电容量可达161 mA.h/g,该材料具有良好的循环性能。XRD物相分析证实,在所有的样品中主要物相是橄榄石相的磷酸亚铁锂,但在较低温度合成的样品中观察到杂相。以L iOH.H2O为100%锂源、于500℃下灼烧24 h,所得样品的衍射花样中可明显地观察到Fe3O4相的几个衍射峰。使用X射线能谱随机测量了样品AA75625不同表面区域的铁磷摩尔比。统计结果表明,测量的铁磷摩尔比的平均值为2.2,样品表面铁磷摩尔比为2.2的95%置信区间为(1.3,3.1)。结果表明,样品表面铁磷分布是不均匀的。分析了该现象的可能成因并指出它导致了容量损失。

Lithium polyacrylate（PAA-Li） prepared in our lab was used as the carbon source and part of the lithium source to synthesize LiFePO4/C. The sample AA75625 synthesized from 75% （molar fraction） PAA-Li and 25% LiOH · H2O displayed a discharge capacity of 161 mA · h/g at the 10th cycle at a current density of 0.04 × 10^-3 A/cm^2 and 20 ℃, showing good cycling performance. It was proved by XRD that the main crystalline phase of all the samples was LiFePO4. lower, and some peaks attributed to Fe3O4 were 500 ℃. The X-ray energy spectrum was used to Impurity was found in the samples calcinated at 550 ℃ or found＇for the sample synthesized by 100% LiOH · H2O at detect the value of Fe： P（ molar ratio） at different randomly chosen areas of the sample AA75625. It was discovered that the molar ratio of Fe to P was inhomogeneous and the average value was 2. 2, while the significance interval was （ 1.3,3.1 ） ; therefore, it deviated from 1 ： 1 significantly, which meant that Fe and P distributed inhomogeneously on the surface of the particles. The probable reason causing the inhomogeneous molar ratio of Fe to P was discussed, and it was pointed out that the phenomenon caused the capacity loss.