Sol-gel and hand milling techniques were used to prepare a lithium iron phosphate-lithium manganese silicate (LiFePO 4 À Li 2 MnSiO 4) hybrid cathode materials. The structural studies from x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) show that the materials are well crystallized although few impurities were observed in the pristine LiFePO 4 (LFP) and Li 2 MnSiO 4 (LMS) materials. We used graphene to coat the hybrid cathode materials in order to increase its conductivity and enhance the electrochemical performance. The successful reduction of the graphene oxide into graphene nanosheets was confirmed with the results from the Fourier transform infrared (FTIR) and Raman spectroscopy. The morphological analysis indicate that the pristine materials are made of spherical nanoparticles that are slightly agglomerated while the sol-gel-prepared hybrid cathode materials show evenly distributed spherical nanoparticles with minimal agglomeration. The in situ sol-gel technique gave more homogenously mixed material in comparison to the hand milling method and particle sizes of 37 and 23 nm respectively were obtained for the plain, and graphenised sol gel derived hybrid materials. The sol-gel derived hybrid materials are also the most thermally stable giving a total weight loss of 4.5 % and 3.4 % for the plain and graphenised cathodes respectively. While the LFP-LMS hybrid cathode materials performed better electrochemically more than the pristine materials in terms of enhanced current and specific capacities, the graphenised LFP-LMS hybrid cathode materials showed better electrochemical properties compared to those without graphene. This is associated with the presence of graphene nanosheets in these samples. All the results confirmed that the graphenised LiFePO 4 À Li 2 MnSiO 4 hybrid cathode material prepared via in situ sol-gel method performed better than those of the hand milling method.
A Li2MnSiO4/Al2O3 nanocomposite (LMSA) was prepared as positive electrode material for aqueous supercapatteries by hydrothermal synthesis of Li2MnSiO4 nanoparticles (LMS) followed by wet chemical coating with Al2O3. Scanning electron microscopy (SEM) mapping of the spherical LMSA nanoparticles indicated a homogenous distribution of the constituent atoms. Small‐angle X‐ray scattering (SAXS) measurements revealed that a prominent population of the nanoparticles show a center‐to‐center spacing of 7 nm. This is resulting in a large surface area accessible for the migration of Li‐ions and efficient charge storage, leading to improved electrochemical performance as a supercapattery electrode. X‐ray diffraction (XRD) and solid‐state nuclear magnetic resonance spectroscopy (SS NMR) studies portrayed the orthorhombic (Pmn21) crystalline phase of the LMSA and LMS materials which provides a good migratory pathway for the Li‐ions. The nanocomposite showed a high rate performance as a positive electrode in an aqueous supercapattery assembled with activated carbon as the negative electrode. The hybrid cell delivered a maximum specific capacitance of 141.5 F g−1 and a maximum specific power of 4020.8 W kg−1 with good cyclic stability and capacitance retention of 93.6 % after 100 cycles. These results the promising potential of the Li2MnSiO4/Al2O3 nanocomposite as candidate for advanced supercapatteries.
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