分级过程对LiFePO_4/C电池性能的影响

Effects of Jet Milling and Classifying Process on the Performance of LiFePO_4/C in Full Batteries

本文采用磷酸铁工艺路线制备碳包覆的磷酸铁锂(LiFePO_4/C)复合正极材料,系统考察了气流粉碎分级过程对LiFePO_4/C正极材料及全电池性能的影响.研究表明,分级前磷酸铁锂颗粒粒度较大,中值粒径为17.37μm,呈规整球形形貌,具有较高的振实密度和碳含量;分级后球形被打碎,振实减小.全电池测试结果显示,分级过程对全电池的容量、交流内阻、直流内阻、功率密度的影响较小;但分级前电芯的低温放电容量保持率和550周的高温循环保持率分别60.1%和87.5%,明显优于分级后的49.5%和84.7%.分级前碳层能均匀包覆在磷酸铁锂表面形成均匀导电网络,而分级过程将磷酸铁锂的碳层有一定的剥离和破坏导致性能下降.

The carbon coated lithium iron phosphate（LiFePO4/C） composite cathode material was prepared by using iron phosphate process.The effects of jet milling and classifying process on the electrochemical performance of LiFePO4/C cathode material in full batteries were investigted.Scanning electron microscopic analyses suggested that the globose secondary particles were crustily crushed during the jet milling and classifying process,which would further result in lower tap density and carbon content.The LiFePO4/C composite cathode materials with different physical characteristics were further tested in full batteries to evaluate the electrochemical properties.The results showed no obvious differences in capacity,AC resistance,DC resistance and power density.However,the globose LiFePO4/C exhibited far better performances in low temperature discharge capacity retention rate and high temperature cycle retention than that of granulated composite cathode,which probably arisen from the certain delamination and destruction of conductive network during the jet milling and classifying process.