In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.
Large scale energy storage system with low cost, high power, and long cycle life is crucial for addressing the energy crisis, especially when integrated with renewable energy resources. To realize grid-scale applications of the energy storage devices, there remain several key issues including the development of low-cost, highperformance materials that are environmentally friendly. This study explores the synergic contribution of the reduced graphene oxide (rGO) on metal organic framework (MOF) as positive electrode for asymmetric supercabattery. The structural elucidation of the synthesised hybrid material and its precursors were characterised using XRD, FTIR, TGA, SEM and TEM. The electrochemical analysis of the synthesised hybrid material and its precursors was achieved using CV, GCD and EIS. The electrochemical behaviour of NF-rGO/MOF hybrid obtained from the three-electrode system exhibited a battery-type behaviour and accomplished an improved specific capacity of 459.0 Cg À 1 at the current density of 1.5 A g À 1. Furthermore, the two-electrode system fabricated in an asymmetric configuration made of NF-rGO/ MOF hybrid as the positive electrode and activated carbon (AC) as the negative electrode studied in 3.0 M KOH electrolyte, exhibited specific capacity of about 48.81 Cg À 1 at the current density of 0.4 A g À 1 , the corresponding maximum energy density of 11.0 Wh kg À 1 and the maximum power density of 640.45 W kg À 1. The cycling stability of the rGO/MOF hybrid asymmetric device displayed 70 % capacity retention after 2000 cycles.
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