Manganese-based cathode materials for zinc-ion and lithium-sulfur batteries

Abstract

Scientists face a challenge in developing new materials that are highly innovative to set a technological precedent while maintaining the application relevance for a substantial timeline. One significant strategy in new material exploration is the advancement of high entropy alloys whereby this field has gained new properties with a high potential for technological implementation. This master’s thesis extends the entropy idea to oxide materials, particularly manganese oxide materials. It also uses microwave irradiation to enhance the properties of these oxides. Firstly, microwave irradiation and hydrothermal synthesis routes were used to synthesize β-MnO2 and α-MnO2 respectively. Physical characterization was done using XRD, SEM, and TGA to investigate the crystallinity, morphology, and thermal stability. According to the TGA results, β-MnO2 showed a higher thermal resistance of 87% compared to α MnO2 whose thermal resistance was 83%. SEM images showed nanorods of β-MnO2 that were bigger and much shorter than the nanowires of α-MnO2. Electrochemical characterizations that included CV, GCD, and EIS were then conducted on aqueous zinc-ion batteries. α-MnO2 showed higher diffusion kinetics which was evident in the CV and EIS analysis while β-MnO2 had better energy storage properties which was portrayed in the GCD analysis. Secondly, we synthesized the novel high-entropy oxide (CoCuMnFeNi)3O4 by Pechini-assisted synthesis. We employed this synthesis technique because it uses low temperatures in the production of pure and homogenous oxides. We performed physical characterization and electrochemical measurements for aqueous zinc-ion batteries. We then incorporated two types of carbon (Ketjen black and Super C45 (carbon black) and determined the electrochemical performance. According to our results, Ketjen black showed an improved performance which we postulated it to its large surface area. Lastly, we employed the HESOx as an electrocatalyst in lithium-sulfur batteries. We synthesized HESOX/OLC/S and OLC/S by melt-diffusion process. OLC/S was employed as a control in the electrochemical characterizations. The results showed that HESOx had higher diffusion kinetics which was achieved from the lower ∆Ep and RCT values. HESOx also had a high capacity retention of 74%. On the other hand, OLC/S had better energy storage capacity shown by its high specific capacity of 523.10 mAhg-1 at 0.1 C.