石墨烯修饰改性制备锂离子电池LiFePO_4/LiNi_(0.8)Co_(0.15)Al_(0.05)O_2复合正极材料及其性能

Synthesis and Properties of LiFePO_4/LiNi_(0.8)Co_(0.15)Al_(0.05)O_2 Composite Cathode Material Modificated by Graphene for Lithium Ion Battery

采用两步干混-球磨方法制备了石墨烯掺杂改性的锂离子电池LiFePO_4/LiNi_(0.8)Co_(0.15)Al_(0.05)O_2复合正极材料,实现LiNi_(0.8)Co_(0.15)Al_(0.05)O_2材料的高容量和高安全性。借助X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)以及电化学测试等表征手段对材料的晶体结构、微观形貌和电化学性能进行了较系统的研究。结果表明,石墨烯的存在实现了Li Fe PO4材料在LiNi_(0.8)Co_(0.15)Al_(0.05)O_2材料表面的完全包覆,形成致密的包覆层,进一步抑制LiNi_(0.8)Co_(0.15)Al_(0.05)O_2与电解液之间的副反应,提高活性材料利用率和循环性能。三者之间构成导电网络,加快电子渗透和传输,提高倍率性能。Li Fe PO4质量分数为20%的Li Fe PO4-Graphene/LiNi_(0.8)Co_(0.15)Al_(0.05)O_2样品具有最佳的容量性能和长循环性能,0.1C时放电容量达到202.5 m Ah·g^(-1),3C时放电容量仍然可保持在160.5 m Ah·g^(-1)。50℃在2.8~4.3 V,0.5C下循环100次后,容量保持率为91.9%,优于LiNi_(0.8)Co_(0.15)Al_(0.05)O_2和LiFePO_4/LiNi_(0.8)Co_(0.15)Al_(0.05)O_2样品的72.9%和82.0%。

The LiFePO4-Graphene/LiFePO4/LiNi0.8Co0.15Al0.05O2 composite for lithium ion batteries has been prepared by a two-step dry-mixing and ball-milling procedure to achieve high capacity and high security of LiFePO4/LiNi0.8Co0.15Al0.05O2.The crystalline structure, morphology and electrochemical performance were systematically characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscope（TEM）, X-ray photoelectronic spectroscopy（XPS） and electrochemical tests. With the addition of graphene, the LiFePO4 nanoparticles can cover the surface of LiFePO4/LiNi0.8Co0.15Al0.05O2 tightly, further protecting LiFePO4/LiNi0.8Co0.15Al0.05O2 from the side reaction with electrolyte, increasing the utilization of active materials and enhancing the cycling performance. The conductive networks consisted of LiFePO4/LiNi0.8Co0.15Al0.05O2, LiFePO4 and graphene can facilitate electron infiltration and transport, thus improving the rate performance. The LiFePO4-Graphene/LiFePO4/LiNi0.8Co0.15Al0.05O2 composite with 20%（w/w） LiFePO4 content exhibits a reversible capacitance up to 202.5 m Ah·g^（-1） at 0.1 C, good rate capability with160.5 m Ah·g^（-1） at 3 C, and an excellent long-term cycling stability with 91.9% capacity retention after 100 cycles at 50 ℃, which is much better than 72.9% of the pristine LiFePO4/LiNi0.8Co0.15Al0.05O2 and 82.0% of the LiFePO4/LiFePO4/LiNi0.8Co0.15Al0.05O2 composite.