M-Oxide (M=Co, Mn Zn)/ Carbon Based Hybrid Electrode Materials for Electrochemical Storage Devices

Abstract

Over the past decades, the increasing cost of fuels, global warming, and the accelerated burning of fossil fuels are the leading concerns on environmental issues and the development of sustainable energy resources. In addition, due to the increasing demand for power supply to wearable and portable electronic devices such as mobile phones, electronic vehicles, and general electronic machines, the construction of storage devices with astonishing energy capacity, improved power density and elongated cycle life has become a crucial demand worldwide. In this regard, high-performance rechargeable batteries for instance, sodium-ion batteries with high energy density are a potential alternative to lithium-ion batteries for use in portable electronics and hybrid electric vehicles. Advantageous utilization of SIBs requires superior performance, enriched with cost-effective anode materials, having excellent storage capability, high conductivity, and structural stability. Their proficient apprehension of having exceptional electrochemical behavior is considered to bridge the hurdles triggered by inadequate resources and costly manufacturing of lithium-ion batteries. Likewise, supercapacitors are devices that are proficient in managing high power densities. With the promising combination of features such as high power density, excellent cyclic stability and high rate capability, environment friendliness, and ability to store and deliver energy at a high rate, supercapacitors meet the requirements of the growing concerns of electronic industry. Hybrid structures based on inorganic metal oxides (Co, Mn, Zn, and Ni) and organic nano-carbons (carbon nanotubes and graphene) are evolving as satisfactory electrode materials for the next-generation sodium-ion batteries and potential supercapacitors owing to their exceptional properties. In this context, Co2.98Zn0.02O4/CNTs hybrid is synthesized using a facile hydrothermal followed by a solvothermal route. As prepared hybrid has been utilized as an anode in a Na half-cell and the results are compared with Co2.98Zn0.02O4 and bare Co3O4 anodes. Galvanostatic charge-discharge profiles revealed a high reversible capacity of 721 mAh g-1 for the electrode containing carbon nanotubes i.e. Co2.98Zn0.02O4/CNTs exhibiting remarkable coulombic efficiency of 99% as compared to the other two electrodes. The hybrid anode showed improved capacity retention (289 mAh g-1) after 100 cycles as computed from the cyclic test which is much higher than bare Co3O4. The rate capability test of Co2.98Zn0.02O4/CNTs showed that vi specific capacity retained as high as 138 mAh g-1@10C which is an outstanding rate performance, whereas bare Co3O4 couldn’t perform even after 0.5C. Sodium insertion/extraction is also improved for Co2.98Zn0.02O4/CNTs, as revealed by electrochemical impedance and diffusion coefficient. From these findings, it is inferred that carbon-based Zn doped Co3O4 hybrid electrode materials can be a superior combination for high-performance and fast charging future sodium-ion batteries. Furthermore, we report a facile synthesis of Ni0.06Co2.94O4/CNTs hybrid using the solvothermal route and Ni0.06Co2.94O4 using the hydrothermal approach. The formation of a nest-like conductive framework of Ni0.06Co2.94O4/CNT composites, aligning favorably to form an assembly of a layered structure, supports an efficient Na-ion insertion/extraction process. A high initial charge capacity of 621 and 582 mAh g-1 is delivered by Ni0.06Co2.94O4/CNTs and Ni0.06Co2.94O4 electrodes, respectively which retained up to 328 and 239 mAh g-1 after 100 cycles. The electrodes also delivered excellent rate performance with 119 and 93 mAh g-1 at 5.0C and retained 77 and 64% of initial capacity, respectively when recovered from 0.05C. Additionally, Ni0.06Co2.94O4/CNTs exhibited low impedance over a wide range of frequencies resulting in more Na ions storage and a faster Na insertion/extraction process. The exceptional performance shown by the hybrid electrode is due to the synergistic influence flanked by binary metal oxides and CNTs. Hence, the hybrid of Ni-doped metal oxide and carbonaceous species emerges as an excellent choice for use as an electrode for electrochemical energy storage devices. Transition metal oxides/graphene nanosheets based materials have been emerging as potential electrodes for supercapacitors. However, their complex synthesis, idiosyncratic microstructure, and manageable conductivity are some challenging tasks of the present era. Herein, we report a strategic hybrid electrode material for supercapacitors to address the challenges related to low energy density without compromising its power density. For this purpose, two hybrid compositions consisting of Mn0.06Co2.94O4 anchored on carbon nanotubes and hydrothermally reduced graphene oxide are synthesized by a facile solvothermal technique, and their electrochemical properties are compared with pure Mn0.06Co2.94O4 and Co3O4. The highly crystalline structure, well-defined, well-ordered, and in particular, electrochemically favorable morphologies are achieved. As a supercapacitor electrode, the graphene-based hybrid vii electrode delivered a high specific capacitance of 933 F/g at a current density of 4 A/g. Further, an exceptional energy density of 55 Wh /kg along with a remarkable power density of 9 kW/kg at 8 A/g has been achieved for HrGO hybrid electrode. Additionally, Mn0.06Co2.94O4 hybrid with CNTs also exhibited brilliant characteristics in terms of energy and power density, where it showed the highest specific capacitance of 950 F/g and remarkable energy density of 33 Wh/kg at 4 A/g but delivered moderate power density. The graphene-based hybrid showed an excellent cyclic life and retained 82% capacitance after 33000 charge-discharge cycles. The phenomenal performance of graphene-based hybrid is attributed to the synergistic effect between metal oxides and highly conductive graphene sheets. Clinging to the features of this important hybrid, this general strategy can be applied to other metal oxides with different carbon derivatives to employ in energy storage applications and beyond. Owing to high capacitance values, TMOs are preferably being utilized for energy storage applications as electrode materials in SCs. However, the electrochemical performance of TMOs is hindered due to less specific surface area and high tendency towards aggregation. Therefore, tuning in electrochemical activity of TMOs is essential. In this framework, NiFe2O4 was prepared using a facile and cost-effective citrate-gel followed by auto-ignition method, and was incorporated with activated carbon contents to tune the electrochemical performance. Formation of inverse spinel structure of NFO and its stability throughout the compositions was examined using X-ray diffraction analysis. Well-dispersed, spherical and porous morphological features were visualized. CV was carried out at constant potential window of 0.25 to 0.65 V and different scan rates (0.009 to 0.08 Vs-1). The pseudo-capacitive behavior was perceived from occurrences of oxidation/reduction peaks. In addition, charge/discharge curves revealed cyclic stability over long range cycles. Specific capacitance, discharge time, energy and power density values were also measured for all the compositions and NFO with 1% activated carbon was found to be the most suitable candidate for use as electrode materials in the present work.