Browsing by Author "Ikpo, Chinwe"
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Item Designing next generation high energy density lithium-ion battery with manganese orthosilicate-capped alumina nanofilm(University of the Western Cape, 2015) Ndipingwi, Miranda Mengwi; Iwuoha, Emmanuel; Ikpo, ChinweIn the wide search for advanced materials for next generation lithium-ion batteries, lithium manganese orthosilicate, Li₂MnSiO₄ is increasingly gaining attention as a potential cathode material by virtue of its ability to facilitate the extraction of two lithium ions per formula unit, resulting in a two-electron redox process involving Mn²⁺/Mn³⁺ and Mn³⁺/Mn⁴⁺ redox couples. This property confers on it, a higher theoretical specific capacity of 333 mAhg⁻¹ which is superior to the conventional layered LiCoO₂ at 274 mAhg⁻¹ and the commercially available olivine LiFePO₄ at 170 mAhg⁻¹. Its iron analogue, Li₂FeSiO₄ has only 166 mAhg⁻¹ capacity as the Fe⁴⁺ oxidation state is difficult to access. However, the capacity of Li₂MnSiO₄ is not fully exploited in practical galvanostatic charge-discharge tests due to the instability of the delithiated material which causes excessive polarization during cycling and its low intrinsic electronic conductivity. By reducing the particle size, the electrochemical performance of this material can be enhanced since it increases the surface contact between the electrode and electrolyte and further reduces the diffusion pathway of lithium ions. In this study, a versatile hydrothermal synthetic pathway was employed to produce nanoparticles of Li₂MnSiO₄, by carefully tuning the reaction temperature and the concentration of the metal precursors. The nanostructured cathode material was further coated with a thin film of aluminium oxide in order to modify its structural and electronic properties. The synthesized materials were characterized by microscopic (HRSEM and HRTEM), spectroscopic (FTIR, XRD, SS-NMR, XPS) and electrochemical techniques (CV, SWV and EIS). Microscopic techniques revealed spherical morphologies with particle sizes in the range of 21-90 nm. Elemental distribution maps obtained from HRSEM for the novel cathode material showed an even distribution of elements which will facilitate the removal/insertion of Li-ions and electrons out/into the cathode material. Spectroscopic results (FTIR) revealed the vibration of the Si-Mn-O linkage, ascertaining the complete insertion of Mn ions into the SiO₄⁴⁻ tetrahedra. XRD and ⁷Li MAS NMR studies confirmed a Pmn21 orthorhombic crystal pattern for the pristine Li₂MnSiO₄ and novel Li₂MnSiO₄/Al₂O₃ which is reported to provide the simplest migratory pathway for Li-ions due to the high symmetrical equivalence of all Li sites in the unit cell, thus leading to high electrochemical reversibility and an enhancement in the overall performance of the cathode materials. The divalent state of manganese present in Li₂Mn²⁺SiO₄ was confirmed by XPS surface analysis. Scan rate studies performed on the novel cathode material showed a quasi-reversible electron transfer process. The novel cathode material demonstrated superior electrochemical performance over the pristine material. Charge/discharge capacity values calculated from the cyclic voltammograms of the novel and pristine cathode materials showed a higher charge and discharge capacity of 209 mAh/g and 107 mAh/g for the novel cathode material compared to 159 mAh/g and 68 mAh/g for the pristine material. The diffusion coefficient was one order of magnitude higher for the novel cathode material (3.06 x10⁻⁶ cm2s⁻¹) than that of the pristine material (6.79 x 10⁻⁷ cm2s⁻¹), with a charge transfer resistance of 1389 Ω and time constant (τ) of 1414.4 s rad⁻¹ for the novel cathode material compared to 1549 Ω and 1584.4 s rad-1 for the pristine material. The higher electrochemical performance of the novel Li₂MnSiO₄/All₂O₃ cathode material over the pristine Li₂MnSiO₄ material can be attributed to the alumina nanoparticle surface coating which considerably reduced the structural instability intrinsic to the pristine Li₂MnSiO₄ cathode material and improved the charge transfer kinetics.Item Graphenised Lithium Iron Phosphate and Lithium Manganese Silicate Hybrid Cathode Systems for Lithium-Ion Batteries(University of the Western Cape, 2017) Myalo, Zolani; Ikpo, ChinweThis research was based on the development and characterization of graphenised lithium iron phosphate-lithium manganese silicate (LiFePO4-Li2MnSiO4) hybrid cathode materials for use in Li-ion batteries. Although previous studies have mainly focused on the use of a single cathode material, recent works have shown that a combination of two or more cathode materials provides better performances compared to a single cathode material. The LiFePO4- Li2MnSiO4 hybrid cathode material is composed of LiFePO4 and Li2MnSiO4. The Li2MnSiO4 contributes its high working voltage ranging from 4.1 to 4.4 V and a specific capacity of 330 mA h g-1, which is twice that of the LiFePO4 which, in turn, offers its long cycle life, high rate capacity as well as good electrochemical and thermal stability. The two cathode materials complement each other's properties however they suffer from low electronic conductivities which were suppressed by coating the hybrid material with graphene nanosheets. The synthetic route entailed a separate preparation of the individual pristine cathode materials, using a sol-gel protocol. Then, the graphenised LiFePO4-Li2MnSiO4 and LiFePO4-Li2MnSiO4 hybrid cathodes were obtained in two ways: the hand milling (HM) method where the pristine cathodes were separately prepared and then mixed with graphene using a pestle and mortar, and the in situ sol-gel (SG) approach where the Li2MnSiO4 and graphene were added into the LiFePO4 sol, stirred and calcined together.Item Graphol and vanadia-link zin doped lithium manganese silicate nanoarchitectonic platforms for supercapatteries(University of the Western Cape, 2020) Ndipingwi, Miranda Mengwi; Iwuoho, Emmanuel; Ikpo, ChinweEnergy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT).Item Graphol and vanadia-linkedzink-doped lithium manganese silicate nanoarchitectonic platforms for supercapatteries(University of Western cape, 2020) Ndipingwi, Miranda Mengwi; Iwuoha, Emmanuel; Ikpo, ChinweEnergy storage technologies are rapidly being developed due to the increased awareness of global warming and growing reliance of society on renewable energy sources. Among various electrochemical energy storage technologies, high power supercapacitors and lithium ion batteries with excellent energy density stand out in terms of their flexibility and scalability. However, supercapacitors are handicapped by low energy density and batteries lag behind in power. Supercapatteries have emerged as hybrid devices which synergize the merits of supercapacitors and batteries with the likelihood of becoming the ultimate power sources for multi-function electronic equipment and electric/hybrid vehicles in the future. But the need for new and advanced electrodes is key to enhancing the performance of supercapatteries. Leading-edge technologies in material design such as nanoarchitectonics become very relevant in this regard. This work involves the preparation of vanadium pentoxide (V2O5), pristine and zinc doped lithium manganese silicate (Li2MnSiO4) nanoarchitectures as well as their composites with hydroxylated graphene (G-ol) and carbon nanotubes (CNT).Item High power asymmetric supercapacitor based on activated carbon/reduced graphene oxide electrode system(Elsevier, 2023-02-22) Dywili, Nomxolisi; Ntziouni, Afroditi; Ndipingwi, Miranda M.; Ikpo, Chinwe; Nwanya, Assumpta C.; Kordatos, Konstantinos; Iwuoha, EmmanuelWe synthesized Graphene oxide (GO) using the modified Hummers method and further reduced to reduced graphene oxide (rGO) using hydrazine monohydrate and ammonia solution. The prepared materials were interrogated using different characterization techniques to determine which of them is more suitable for supercapacitor application. High resolution scanning electron microscopy (HRSEM) revealed a sheet-like morphology of separated thin sheets and wrinkled edges for GO, whereas rGO consist of thinner sheets with smaller pores than GO. The structural studies as elucidated from X-ray diffraction (XRD) shows that the GO has more interlayer spacing due to a higher oxygen content as compared to the rGO. The oxygen containing functional groups seen in GO either disappear or are greatly reduced in intensity in rGO as evidenced from the Fourier transform infrared spectroscopy (FTIR) of the materials. The electrochemical studies indicate that the rGO gave a higher current response compared to GO and a specific capacitance of 105.3 and 56.7 F g 1 respectively was delivered by rGO and GO at a scan rate of 10 mV s 1 in a three-electrode set-up. Asymmetric supercapacitor cells using GO and rGO as positive electrodes and activated carbon as the negative electrodes gave the highest specific capacitance value of 94.3 F g 1 for the AC//rGO cell and 59.6 F g 1 for the AC//GO cell at a current load of 0.25 A g 1. The specific capacitance obtained from the AC//rGO is comparable to most recorded values for rGO electrodes. A high specific power of 6411.7 W kg 1 was obtained at a specific energy of 22.6 W h kg 1 while at a specific energy of 25.7 W h kg 1, a specific power of 700.1 W kg 1 was obtained for the AC//rGO. This is due to the more porous and thinner sheet of the rGO. The overall results showed that the rGO gave better supercapacitive properties than the GO.Item High power asymmetric supercapacitor based on activated carbon/reduced graphene oxide electrode system.(2023-01) Dywili, Nomxolisi; Ndipingwi, Miranda M.; Ikpo, Chinwe; Nwanya, Assumpta C.; Iwuoha, Emmanuel; Ntziouni, Afroditi; Kordatos, KonstantinosWe synthesized Graphene oxide (GO) using the modified Hummers method and further reduced to reduced graphene oxide (rGO) using hydrazine monohydrate and ammonia solution. The prepared materials were interrogated using different characterization techniques to determine which of them is more suitable for supercapacitor application. High resolution scanning electron microscopy (HRSEM) revealed a sheet-like morphology of separated thin sheets and wrinkled edges for GO, whereas rGO consist of thinner sheets with smaller pores than GO. The structural studies as elucidated from X-ray diffraction (XRD) shows that the GO has more interlayer spacing due to a higher oxygen content as compared to the rGO. The oxygen containing functional groups seen in GO either disappear or are greatly reduced in intensity in rGO as evidenced from the Fourier transform infrared spectroscopy (FTIR) of the materials. The electrochemical studies indicate that the rGO gave a higher current response compared to GO and a specific capacitance of 105.3 and 56.7 F g−1 respectively was delivered by rGO and GO at a scan rate of 10 mV s−1 in a three-electrode set-up. Asymmetric supercapacitor cells using GO and rGO as positive electrodes and activated carbon as the negative electrodes gave the highest specific capacitance value of 94.3 F g−1 for the AC//rGO cell and 59.6 F g−1 for the AC//GO cell at a current load of 0.25 A g−1. The specific capacitance obtained from the AC//rGO is comparable to most recorded values for rGO electrodes. A high specific power of 6411.7 W kg−1 was obtained at a specific energy of 22.6 W h kg−1 while at a specific energy of 25.7 W h kg−1, a specific power of 700.1 W kg−1 was obtained for the AC//rGO. This is due to the more porous and thinner sheet of the rGO. The overall results showed that the rGO gave better supercapacitive properties than the GO.Item High stability asymmetric supercapacitor cell developed with novel microwave-synthesized graphene-stabilized ruthenium antimonide nanomaterial(Elsevier, 2023-02-06) Ekwere, Precious; Ndipingwi, Miranda; Ikpo, Chinwe; Yussuf, Sodiq; Nwambaekwe, Kelechi; Uhuo, Onyinyechi; Iwuoha, EmmanuelRuthenium antimony oxide (RuSbO), and ruthenium antimony oxide graphene (RuSbO-G) nanomaterial was synthesized via the microwave-assisted method for the first time and tested as a possible electrode material for an asymmetric supercapacitor device. The formation of the nanocomposites was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images where the RuSbO material showed randomly distributed spherically shaped nanoparticles, and the RuSbO-G showed ruthenium and antimony nanoparticles scattered randomly on the graphene sheets. The SEM-electron dispersion X-ray spectroscopy (SEMEDS) showed significant proof for nanoparticle formation with the elemental composition, while the X-ray photoelectron spectroscopy confirmed the oxidation states of the elements present. Both materials were further characterized in a three-electrode cell setup using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) and their electrochemical properties were compared to establish their suitability for energy storage purposes. From the result, different double layer properties were shown by the RuSbO and RuSbO-G in the 1 M Li2SO4 electrolyte. When compared to the RuSbO electrode, the composite had greater energy storage capabilities with a maximum capacitance of 289.47 F g 1 at 0.1 A g 1 current load. An efficiency of ~100 % was reached at a current density of 0.5 A g 1. Subsequently, both materials were used to fabricate a portable asymmetric supercapacitor. The RuSbO-G device yielded a maximum specific capacitance of 167.96 F g 1, resulting in an energy density of 75.58.0 W h kg 1 at a power density of 360 W kg 1 at 0.1 A g 1 current load, with ~100 % charge retention after 4900 cycles. This study turns a new research light on RuSbO based materials as an energy storage material for supercapacitors.Item Nanoparticles-infused lithium manganese phosphate coated with magnesium-gold composite thin film - a possible novel material for lithium ion battery olivine cathode.(University of the Western Cape, 2014) Hlongwa, Ntuthuko Wonderboy; Iwuoha, Emmanuel I.; Ikpo, ChinweArchitecturally enhanced electrode materials for lithium ion batteries (LIB) with permeable morphologies have received broad research interests over the past years for their promising properties. However, literature based on modified porous nanoparticles of lithium manganese phosphate (LiMnPO₄) is meagre. The goal of this project is to explore lithium manganese phosphate (LiMnPO₄) nanoparticles and enhance its energy and power density through surface treatment with transition metal nanoparticles. Nanostructured materials offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The material can store lithium ions but have large structure change and volume expansion during charge/discharge processes, which can cause mechanical failure. LiMnPO₄ 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. Ag/AgCl which falls within the electrochemical stability window of conventional electrolyte solutions. LiMnPO₄ has safety features due to the presence of a strong P–O covalent bond. The LiMnPO₄ nanoparticles were synthesized via a sol-gel method followed by coating with gold nanoparticles to enhance conductivity. A magnesium oxide (MgO) nanowire was then coated onto the LiMnPO₄/Au, in order to form a support for gold nanoparticles which will then form a thin film on top of LiMnPO₄ nanoparticles crystals. The formed products will be LiMnPO₄/Mg-Au composite. MgO has good electrical and thermal conductivity with improved corrosion resistance. Thus the electronic and optical properties of MgO nanowires were sufficient for the increase in the lithium ion diffusion. The pristine LiMnPO₄ and LiMnPO₄/Mg-Au composite were examined using a combination of spectroscopic and microscopic techniques along with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiMnPO₄/Mg-Au composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiMnPO₄ due to the presence of the conductive additives in the LiMnPO₄/Mg-Au composite. This is demonstrated in the values of the diffusion coefficient (D) and the values of charge and discharge capacities determined through cyclic voltammetry. For the composite cathode, D= 2.0 x 10⁻⁹ cm²/s while for pristine LiMnPO₄ D = 4.81 x 10⁻¹⁰ cm2/s. The charge capacity and the discharge capacity for LiMnPO₄/Mg-Au composite were 259.9 mAh/g and 157.6 mAh/g, respectively, at 10 mV/s. The corresponding values for pristine LiMnPO₄ were 115 mAh/g and 44.75 mAh/g, respectively. A similar trend was observed in the results obtained from EIS measurements. These results indicate that LiMnPO₄/Mg-Au composite has better conductivity and will facilitate faster electron transfer and therefore better electrochemical performance than pristine LiMnPO₄. The composite cathode material (LiMnPO₄/Mg-Au) with improved electronic conductivity holds great promise for enhancing electrochemical performances, discharge capacity, cycle performance and the suppression of the reductive decomposition of the electrolyte solution on the LiMnPO₄ surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiMnPO₄ nanopowder cathode material.Item Supercapacitor development from transition metal-integrated spinel manganese oxide-carbon nanotubes composite materials(University of the Western Cape, 2019) Nolly, Christopher; Ikpo, ChinweSupercapacitors are electrochemical energy storage devices, much like Li-ion batteries, that have expeditiously been improved over the years through extensive research conducted in material sciences and nanotechnology. Since supercapacitors are mostly known for their high power densities and extended lifecycle, they are therefore mainly employed in applications where large quantities of energy is required to be stored and/or released within quick time periods and energy outputs. In the modern technological era, supercapacitors are predominantly employed in hybrid electric vehicles (HEVs), trains, trams, cranes, cell phones, as uninterrupted power supplies (UPS devices), and in memory backup units for computer systems. Apart from these conventional application areas, the application field of energy storage that ultimately makes supercapacitors blossom, is the field of storing harvested renewable energy from self-sustaining power sources such as solar cells and/or wind turbines. However, the unfortunate disadvantage associated with supercapacitors is its low energy density compared to batteries. Therefore, this research work presents the study of multi-walled carbon nanotubes (MWCNTs) integrated with spinel nanostructured CuMn2O4 nanoparticles as composite electrode materials towards enhancing the energy performance in asymmetric pseudocapacitors. The hybrid composite (CuMn2O4/MWCNT) development process initially started with the synthesis of the pristine (hausmannite-type) Mn3O4 material, upon modification thereafter with copper and carbon nanoparticles.