复合导电添加剂对磷酸铁锂电池性能的影响

Performance of LiFePO_4-Based Battery with Compound Conductive Additives

磷酸铁锂基锂离子电池由于具有高的安全性能和优异的循环性能是新能源领域的研究热点。而磷酸铁锂材料本身导电性差,在实体电池制作过程中容易出现内阻较大和倍率性能不佳等问题,因此需要研究导电添加剂组成对电池性能的影响。本文用商业化的LiFePO4、石墨和电解液为主要原料,以碳纳米管(CNT)和导电碳黑(Super P)为导电添加剂,制作了20 Ah容量兼倍率型的磷酸铁锂软包电池。扫描电镜(SEM)分析测试表明导电碳黑Super P和CNT分散均匀,可与磷酸铁锂颗粒形成点和线的接触,进而可以提供更多的附加导电通路。应用该复合导电添加剂所制作的磷酸铁锂动力电池具有1.0 mΩ内阻,电池首次效率在91%以上,正极材料克容量0.5C发挥到146.32 mAh·g-1,9C/1C接近100%,倍率性能优异,电芯经过2165周循环电池容量保持率为91.78%,循环性能优秀;而使用常规导电碳SP+KS-6的分容比容量是139.06 mAh·g-1,电池内阻均值为3.25 mΩ,电芯经过2003次循环,容量保持率为87.63%。经过优化实验条件,正极中添加3%SP+1%KS-6+1%CNT复合导电剂的电芯整体性能最佳。

Lithium iron phosphate （ LiFePO4 ） based lithium ion batteries with the advantages of good safety and long cycle life was a hot area in new energy field. The problems of larger internal resistance （IR） and poor rate capability were easy to be found in the full battery production process because of itself poor conductivity. It was necessary to study the effect of conductive additives on the battery performance. A LiFePO4 type lithium secondary batteries cell of 20 Ah capacity with a high energy density and power density was de- veloped by the commercial of LiFePO4 cathode, graphite and electrolyte as the main raw material, and carbon nanotubes （CNT） and Super P as conductive additives. Scanning electron microscope （SEM） analysis showed that the conductive carbon black Super P and CNT could disperse uniformly, and could form point and line contacted with the grain particles of LiFePO4, which could provide more additional conductive paths. The lithium iron phosphate battery had only 1.0 mΩ resistance by the application of the compound con-ductive additives. And the first reversible efficiency reached 91%. The cathode had the specific capacity of 146.32 mA.g-1 at 0. 5C rate. Furthermore, the cell showed good rate performance with the 9C/1C close to 100%. The battery showed good cyclic capability with capacity retention ratio of 91.78% after 2165 cycles. The cell with the conventional conductive carbon SP ＋ KS-6 additives had the specific capacity of 139.06 mAh.g-1 , and the average internal resistance was 3.25 mΩ The cell showed capacity retention ratio of 87.63 % after 2003 cycles. After optimizing the experimental conditions, the cell with 3 % SP ＋ 1% KS-6 ＋ 1% CNT composite conduc- tive agent in the cathode showed the best performance.