聚吡咯包覆FeCl3-石墨层间化合物的制备与电化学储钠性能

以FeCl₃和天然鳞片石墨为原料，通过融盐法制得1阶FeCl₃插层的石墨层间化合物(FeCl₃-GIC)。用原位聚合法对FeCl₃-GIC进行聚吡咯(PPy)包覆改性，形成具有核壳结构的(FeCl₃-GIC)@PPy复合材料。通过多种表征方法研究聚吡咯包覆前后FeCl₃-GIC的表面形貌和微观结构变化。结果表明:聚吡咯均匀致密地包覆在十微米级的FeCl₃-GIC颗粒外部，包覆层厚度为35 nm，经过聚吡咯包覆后(FeCl₃-GIC)@PPy的导电性能显著提高((FeCl₃-GIC)@PPy粉末电阻率2.3×10?3 Ω·cm，FeCl₃-GIC粉末电阻率3.1×10?3 Ω·cm)。采用多种电化学测试探究产物的钠离子存储特性，聚吡咯外壳能够显著提高FeCl₃-GIC作为钠离子电池负极材料的充放电容量、倍率性能和循环性能。在0.1 A·g?1电流密度下循环100次后，FeCl₃-GIC的比容量逐渐衰减到157 mA·h·g?1，而(FeCl₃-GIC)@PPy材料的比容量达到281 mA·h·g?1左右且容量基本保持不变；在电流密度1 A·g?1的条件下循环500次后，(FeCl₃-GIC)@PPy的比容量仍有181 mA·h·g?1，容量保持率约为89%。 

Preparation and electrochemical sodium storage performance of polypyrrole coated FeCl3-intercalated graphite intercalation compound

The 1-stage FeCl₃-intercalated graphite intercalation compound (FeCl₃-GIC) were prepared by a molten salt method using FeCl₃ and natural flake graphite as raw materials. Subsequently, a conductive layer of polypyrrole (PPy) were uniformly coated on the surface of the FeCl₃-GIC particles by in-situ polymerization to form a core-shell structured (FeCl₃-GIC)@PPy composite material. Various characterization methods were employed to study the surface morphology and microstructure evolution of FeCl₃-GIC before and after polypyrrole coating. The results show that a uniform and dense polypyrrole layer with a thickness of 35 nm is tightly coated on the surface of the micro-sized FeCl₃-GIC particles. After coating, the conductivity of the (FeCl₃-GIC)@PPy composite is significantly improved for the powder resistivity is reduced from 3.1×10?3 Ω·cm of FeCl₃-GIC to 2.3×10?3 Ω·cm of (FeCl₃-GIC)@PPy. As an anode material for sodium ion storage, it is found that the (FeCl₃-GIC)@PPy anode exhibits the improved reversible capacitiy, rate capability and cycling stability compared with the naked FeCl₃-GIC anode. Specially, the specific capacity of (FeCl₃-GIC)@PPy remains steady with a high sodium storage value of 281 mA·h·g?1 after 100 cycles at the current density of 0.1 A·g?1, while the FeCl₃-GIC anode shows a continuous capacity decay with a low value of 157 mA·h·g?1 after 100 cycles. Additionally, even at a high current density of 1.0 A·g?1, the (FeCl₃-GIC)@PPy anode delivers a remained sodium storage capacity of 181 mA·h·g?1 after 500 cycles, accompanying with a fascinating capacity retention ratio of 89%.