Ammonium Ion Assisted Preparation Of Manganese Oxides And Their Application In Aqueous Zinc Ion Batteries

Energy has a significant strategic importance in modern society and military development.It serves as a crucial foundation for national economics,national security,and the achievement of sustainable development.Developing high-security and environmentally friendly energy storage technologies is an urgent task.Among the many multivalent metal ion batteries,zinc ion batteries are outstanding for their excellent performance.Manganese-based compounds are preferred by researchers due to their green and multivalent nature as well as their polycrystalline form.However,their large-scale application in practical production is still limited by problems such as manganese dissolution,poor conductivity,and structural transformations.Ion doping and structural design are the most commonly used methods to enhance the performance of manganese-based oxide cathode materials.Currently,metal cation doping and the rational design of nanostructures are the most mature approaches.Nevertheless,the metal cations that play a"pillar"role have significant spatial effects and strong electrostatic interactions,and further research is necessary to enhance the electrochemical performance of batteries.The huge surface area of nanostructures leads to the rapid dissolution of manganese,which needs to be addressed promptly.In view of the above problems,this paper takes Mn O₂ as the research object,and uses different preparation processes and structure design methods to modify Mn O₂,and prepares a manganese-based compound cathode material with good performance for aqueous zinc-ion batteries.The specific content is as follows:（1）The study focuses on the preparation of manganese dioxide with ammonium ion doping via a hydrothermal method（NH₄⁺-MO）and its performance as a zinc storage material.Using KMn O₄ as the manganese source and（NH₄）₂SO₄ as the doping agent,NH₄⁺-MO was synthesized through a simple one-step hydrothermal process,and the impact of hydrothermal temperature and NH₄⁺dosage on Mn O₂ structure,morphology,and electrochemical performance were investigated.Results indicate that hydrothermal temperature and NH₄⁺addition significantly impact the morphology and crystal type of Mn O₂.As the temperature increases,the Mn O₂ morphology changes from folded to nano-flowers,nano-rods,and finally double-cone-shaped microparticles.At 120℃,NH₄⁺addition induces a significant change in Mn O₂ morphology,from folded microparticles to nano-flower-shaped nanospheres.Successful NH₄⁺doping acts as a support to the primary structure,stabilizing theα-Mn O₂（2×2）&（1×1）tunnel structure.The resulting NH₄⁺-MO electrode material exhibits excellent electrochemical performance,with a high reversible specific capacity of 253.5 m Ah g^-1 after 100 cycles at a current density of 0.2A g^-1 and a capacity retention rate of 80.25%after 500 cycles at a high current density of1 A g^-1,demonstrating good cycling stability.（2）In this study,ammonium ion-doped manganese dioxide（NH₄⁺-MO*）was synthesized through a simple co-precipitation method at room temperature,using low-cost Mn Cl₂·4H₂O as the manganese source and reducing agent,H₂O₂ as the oxidizing agent,and NH₃?H₂O as the dopant.The resulting material,4-NH₄⁺-MO*,possessed a blocky morphology with a porous structure and abundant mesopores,exhibiting excellent electrochemical performance.Specifically,when 4 m L of NH₃·H₂O was added,the material demonstrated a large surface area and abundant mesoporous structure.After 100cycles at a current density of 200 m A·g^-1,the material retained a capacity of 218.8 m Ah·g^-1.Additionally,at a current density of 1 A·g^-1,the capacity retention was 66.1%,which indicates good cycling stability.（3）This paragraph discusses the preparation of nanospheres with a core-shell structure made of manganese dioxide（Mn O₂@Mn O₂ NSs）and their zinc storage properties.The nanospheres were prepared using a room temperature template method.Mn SO₄·H₂O was used as the manganese source,while Na HCO₃ and NH₃?H₂O were used as precipitants to obtain Mn CO₃ templates in the form of spherical particles.The obtained Mn CO₃ particles were then used as a template to prepare the Mn O₂@Mn O₂ NSs material using KMn O₄ as the manganese source and hydrochloric acid as the etching agent.The generation of CO₂ during the preparation process facilitated the formation of a porous structure.The gap between the Mn O₂ core and Mn O₂ shell provided buffer space to accommodate the volume expansion and contraction of the core and shell during charging and discharging processes.The resulting nanospheres demonstrated good cyclic stability,with a capacity retention of 178.9 m Ah g^-1 after 100 cycles at a current density of 200m Ag^-1 and a capacity retention rate of 57.4%at 1 A g^-1.