Abstract
In this study, micro/nanoscale LiFePO4/graphene composites are synthesized successfully using a one-step microwave heating method. One-step microwave heating can simplify the reduction step of graphene oxide and provide a convenient, economical, and effective method of preparing graphene composites. The structural analysis shows that LiFePO4/graphene has high phase purity and crystallinity. The morphological analysis shows that LiFePO4/graphene microspheres and micron blocks are composed of densely aggregated nanoparticles; the nanoparticle size can shorten the diffusion path of lithium ions and thus increase the lithium-ion diffusion rate. Additionally, the graphene sheets can provide a rapid transport path for electrons, thus increasing the electronic conductivity of the material. Furthermore, the nanoparticles being packed into the micron graphene sheets can ensure stability in the electrolyte during charging and discharging. Raman analysis reveals that the graphene has a high degree of graphitization. Electrochemical analysis shows that the LiFePO4/graphene has an excellent capacity, high rate performance, and cycle stability. The discharge capacities are 166.3, 156.1, 143.0, 132.4, and 120.9 mAh g−1 at rates of 0.1, 1, 3, 5, and 10 C, respectively. The superior electrochemical performance can be ascribed to the synergy of the shorter lithium-ion diffusion path achieved by LiFePO4 nanoparticles and the conductive networks of graphene.
Highlights
Energy and materials, important pillars of the modern developing society, are closely related to human civilization
The results manifest that the synthetic composites have high crystallinity and purity; this is mainly because microwave synthesis has the advantage of increasing the crystallinity and purity of products
All of the results demonstrate that LiFePO4/graphene composites have better rate performance and cycling stability
Summary
Important pillars of the modern developing society, are closely related to human civilization. Small particle size can decrease the migration distance of lithium ions from the interior to the surface and increase the diffusion rate (Lim et al, 2008; Hai et al, 2019; Li et al, 2019; Xiao et al, 2019). Micro/nanoscale LiFePO4/graphene composites are synthesized successfully using a one-step microwave heating method. The synthesized micro/nanoscale LiFePO4/graphene composites with fine particle size and uniform distribution can decrease the migration distance of lithium ions from the interior to the surface and increase the diffusion rate. The effects of graphene and microwave irradiation on the electrochemical performance of LiFePO4/graphene cathode materials for lithium-ion batteries are further investigated. The cathode electrodes were prepared by mixing 80 wt% active materials (LiFePO4/graphene or LiFePO4/C) and 10 wt% carbon black (TIMCAL) with 10 wt% polytetrafluoroethylene (PTFE, Aldrich) in isopropyl alcohol solution (99.5%, Aldrich). Electrochemical impedance spectroscopy (EIS) profiles were obtained at the same open-circuit voltage by applying a 5-mV amplitude of the AC voltage with the frequency ranging from 100 kHz to 0.01 Hz
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