Synthesis of LiFePO4/graphene microspheres while avoiding restacking of graphene sheet’s for high-rate lithium-ion batteries

• Published in: Journal of industrial and engineering chemistry (Seoul, Korea) 2017, 52(0), , pp.251-259
• Main Authors: Kim, Myeong-Seong, Lee, Geon-Woo, Lee, Suk-Woo, Jeong, Jun Hui, Mhamane, Dattakumar, Roh, Kwang Chul, Kim, Kwang-Bum
• Format: Article
• Language: English
• Subjects: Energy efficiency; Graphene based composite; High performance cathode materials; High-rate lithium ion batteries; Restacking of graphene; 화학공학
• ISSN: 1226-086X; 1876-794X
• DOI: 10.1016/j.jiec.2017.03.054

To fully exploit the properties of graphene as an electrode material for energy storage devices, it is important to prevent the restacking of graphene sheets. In this study, three-dimensional (3D) micro-spherical LiFePO4/graphene composites were synthesized while avoiding the restacking of graphene sheets using a scalable, facile, and simple spray-drying process and a subsequent heat treatment. In this system, the LiFePO4 nanoparticles acted not only as the active material but also as the spacer between the graphene sheets. To determine an optimal condition for preventing the restacking of graphene sheets in the composites, we controlled the weight ratio of LiFePO4 to graphene. During this process, the degree of restacking of graphene sheets in the composites had a significant effect on their morphology and electrochemical properties. The 3D LiFePO4/graphene microspheres were micrometer-sized spherical assemblies with 100nm-sized LiFePO4 nanoparticles and graphene sheets. The microspheres exhibited a high specific capacity of 163mAhg−1 at 0.1 C-rate, excellent rate capability (65% of the initial discharge capacity (0.1 C-rate) at 30 C-rate), and good cycling stability (81.6% capacity retention after 1000 cycles). [Display omitted] •LFP/graphene composite was synthesized while avoiding graphene sheets restacking.•Degree of graphene sheets restacking affected the rate capability of the composites.•Restacked graphene sheets blocked Li ion movement in the electrode.•LFP/graphene composite exhibited improved rate capability and cyclability. LiFePO4/graphene microspheres are synthesized while avoiding the restacking of graphene sheets using a spray-drying process and a subsequent heat treatment. To determine an optimal condition for preventing the restacking of graphene sheets in the composites, we control the weight ratio of LiFePO4 to rGO. When the amount of rGO in the composite exceeds a specific amount, the rGO sheets are spontaneously restacked. The restacked rGO sheets impede the Li ion movement, which is leading to the deterioration of the electrochemical performance at high C-rates. The microspheres synthesized exhibit a high specific capacity, excellent rate capability, and good cycling stability.