Li2MnSiO4/C/Graphene composite as a high performance cathode material for li-ion batteries

Among different cathode materials, the lithium orthosilicates, Li2MSiO4, have unique properties, such as high theoretical capacity of ) 300 mAhg-1), plausible extraction of more than one Li+ ion per formula unit and high thermal stability through strong Si-O bonding[1]. Among the silicate groups, Li2MnSiO4 are more attractive than other counterparts because they are more cost effective and environmentally benign .in addition, Li2MnSiO4 provides a high cell voltage due to the possible oxidation of the Mn3+/Mn4+ couple [1-4]. Li2MnSiO4/C samples were prepared by a citric acid assisted sol–gel method. Graphene oxide prepared by a modified Hummer’s method [5,6]. For the preparation of working electrodes, 90 wt% Li2MnSiO4/C/Graphene-carbon black composites (20% carbon contents) and 10 wt% polyvinylidene fluoride binder were mixed with N-methyl-2-pyrrolidinone. Synthesized materials were characterized by X-ray diffraction (XRD) techniques and we finally have synthesized carbon coated LMS/C-Graphene composite by sol-gel method associated with citric acid, TEOS and Lithium and manganese acetate. Besides providing carbon wiring, GAL aids the gelling process, reduces particle agglomeration during annealing and promotes phase purity. The LMS/(C/RGO) shows an improved electronic conductivity due to the conductive network formed by reduced graphene oxide nanosheets and amorphous carbon in particles. Electrochemical characterizations results indicate high increased reversible capacity of 301 mAhg-1 with a high initial columbic efficiency, and a high discharge capacity at current rate of 0.5 C. that’s double value Compared with LMS/C – carbon black composite, the LMS/(C/RGO) electrode exhibits 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 221 higher capacity and better cycling stability. The first charge and discharge capacities of Li2MnSiO4/C-graphene composite are 455.1 mAhg-1 and 300.7 mAhg-1, respectively, which indicates an initial columbic efficiency of 66.1%. The Li2MnSiO4/C-carbon black composite electrode exhibits similar charge capacity (433.6 mAhg-1) with that of the Li2MnSiO4/C -graphene composite electrode. However, its initial discharge capacity (237.1 mAhg-1) and columbic efficiency (54.7%) were much lower than those of the Li2MnSiO4/C - graphene composite. The improved performance can be contributed to the, reduced crystal size, good particle dispersion, and the improved conductive network between LMS particles.