Browsing by Author "Sifuba, Sabelo"

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    Electrochemical analysis of architecturally enhanced LiFe0.5Mn0.5PO4 multiwalled carbon nanotube composite
    (Hindawi, 2021) Sifuba, Sabelo; Willenberg, Shane; Feleni, Usisipho
    In this work, the effect of carbon on the electrochemical properties of multiwalled carbon nanotube (MWCNT) functionalized lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials, a systematic study based on a combination of structural and spectroscopic techniques was conducted. The phosphor-olivine LiFe0.5Mn0.5PO4 was synthesized via a simple microwave synthesis using LiFePO4 and LiMnPO4 as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe0.5Mn0.5PO4 redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn2+/Mn3+ (4.1 V vs Li/Li+) and Fe2+/Fe3+ (3.5 V vs Li/Li+) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe0.5Mn0.5PO4-MWCNTs have high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulate faster electron transfer and stability for the LiFe0.5Mn0.5PO4 framework, which demonstrates to be favorable as a host material for Li+ ions.
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    Electrochemically enhanced ferric lithium manganese phosphate / multi-walled carbon nanotube, as a possible composite cathode material for lithium ion battery
    (University of the Western Cape, 2019) Sifuba, Sabelo; Ross, Natasha; Iwuoha, Emmanuel; Feleni, Usisipho
    Lithium iron manganese phosphate (LiFe0.5Mn0.5PO4), is a promising, low cost and high energy density (700 Wh/kg) cathode material with high theoretical capacity and high operating voltage of 4.1 V vs. Li/Li+, which falls within the electrochemical stability window of conventional electrolyte solutions. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of its electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion at the surface of the LiFe0.5Mn0.5PO4 particles. Nanostructured materials offered advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The LiFe0.5Mn0.5PO4 nanoparticles were synthesized via a simple-facile microwave method followed by coating with multi-walled carbon nanotubes (MWCNTs) nanoparticles to enhance electrical and thermal conductivity. The pristine LiFe0.5Mn0.5PO4 and LiFe0.5Mn0.5PO4-MWCNTs composite were examined using a combination of spectroscopic and microscopic techniques along with electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiFe0.5Mn0.5PO4-MWCNTs composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiFe0.5Mn0.5PO4 due to the presence of the conductive additives in the LiFe0.5Mn0.5PO4-MWCNTs composite. For the composite cathode, D = 2.0 x 10-9 cm2/s while for pristine LiFe0.5Mn0.5PO4 D = 4.81 x 10-10 cm2/s. The charge capacity and the discharge capacity for LiFe0.5Mn0.5PO4-MWCNTs composite were 259.9 mAh/g and 177.6 mAh/g, respectively, at 0.01 V/s. The corresponding values for pristine LiFe0.5Mn0.5PO4 were 115 mAh/g and 44.75 mAh/g, respectively. This was corroborated by EIS measurements. LiFe0.5Mn0.5PO4-MWCNTs composite showed to have better conductivity which corresponded to faster electron transfer and therefore better electrochemical performance than pristine LiFe0.5Mn0.5PO4. The composite cathode material (LiFe0.5Mn0.5PO4-MWCNTs) with improved electronic conductivity holds great promise for enhancing electrochemical performances and the suppression of the reductive decomposition of the electrolyte solution on the LiFe0.5Mn0.5PO4 surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiFe0.5Mn0.5PO4 nano-powder cathode material.