Synthesis and electrochemical performance comprehensive teaching experimental design of MnO2 cathode material for aqueous zinc-ion batteries
[Objective]To broaden the horizon of college students and help develop their innovative thinking and problem-solving abilities,a comprehensive teaching experiment of δ-MnO2 cathode material for aqueous zinc-ion batteries(AZIBs)was designed.These batteries have increasingly gained attention in the field of large-scale energy storage due to their low cost,high safety standards,and environmental friendliness.The cathode of AZIBs typically provides the active sites for zinc storage,crucially influencing the battery potential and capacity.In this regard,there is a great need to explore modified or novel cathode materials with high capacity and long cycle lifetime.Manganese dioxide(MnO2)has attracted much attention due to its high operating voltage and low manufacturing cost;however,the inherent poor conductivity and structural collapse during charging and discharging of MnO2 cathode led to its low specific capacity and poor cycling stability,which seriously constrain the development of AZIBs.By investigating the related literature,morphological modulation is expected to improve the electrochemical performance and long-term cycling stability of MnO2 cathode materials.[Methods]In this study,existing scientific research equipment was used to design a series of comprehensive tests for battery cathode materials,including the preparation and characterization of materials,the setting of electrochemical tester parameters,and the screening of data.To cultivate students'ability in independent thinking,communication and collaboration,analysis,and problem-solving skills,the experimental data analysis is combined into the process of teaching experiments,such as students observing the morphology of the samples through SEM,analyzing the information of the crystal structure by XRD,testing the electrochemical data by the electrochemical workstation,collaborating with classmates to discuss the analysis and processing of the data,as well as learning the principle of testing instruments and completing the experimental tests in the classroom to ensure the quality of the experimental teaching.[Results]The results showed that δ-MnO2 exhibited excellent rate performance.The cycle stability of δ-MnO2 materials was explored by long-cycle charge-discharge tests at current densities of 0.2 and 1.0 A·g-1.After 50 cycles,the capacity gradually increased due to the oxidation of Mn2+pre-added in the electrolyte to Mn-O compounds during charging.After 120 cycles,the specific capacity increased to 257.7 mAh·g-1,and the capacity retention rate exceeded 100%,indicating that δ-MnO2 material has good cycling performance.At the current density of 1.0 A·g-1,the capacity retention ratio is also over 100%compared with the initial discharge capacity.Then,the reaction process and solid-state diffusion kinetics of δ-MnO2 were studied by the GITT technique.In the discharge test,Zn2+was continuously embedded in the cathode material.It is found that the diffusion coefficients of the high-voltage and low-voltage regions are quite different,which is caused by the migration of two different ions(H+and Zn2+)into the cathode electrode,proving that the intercalation mechanism is different between the two regions.Analyzing the experimental results helps students develop their logical thinking skills.[Conclusions]Based on the cutting-edge technology of the morphology design of Birnessite-type δ-MnO2 cathode materials for AZIBs,this design aims to be a comprehensive,innovative,and operable electrochemical experiment that not only broadens students'horizons but also cultivates their innovative thinking and problem-solving abilities,which is conducive to achieving the goal of cultivating high-quality applied talent.
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