Preparation And Performance Study Of Hierarchical Mn₃O₄/Graphene Micro-Flowers For Alkali Metal Ion Storage

Currently,the increasing demand for new green energy sources is promoting the development of large-scale energy storage systems?LSESSs?.Lithium ion batteries have been widely used in military and civilian small appliances due to their advantages such as high specific energy,high battery voltage,wide operating temperature range,and long storage life.Therefore lithium-ion batteries are ideal for LSESSs.At present,commercial lithium ion batteries with graphite as the cathode material can no longer meet people's needs for high energy density,long cycle life and fast charge and discharge.Therefore,the development of new cathode materials to replace the traditional graphite materials has become the one of focus of current research in this field.Transition metal oxides are considered promising candidates because they offer a reversible capability approximately 2 to 3 times greater than conventional graphite,while being eco-friendly,corrosion resistant,and cost-effective.Moreover,in addition to the material type,the structure of the material itself also has a great influence on the electrochemical performance.By designing reasonable nanostructures,the ionic diffusion distance can be shortened and a continuous electronic transmission path can be provided,which greatly improves the electrochemical performance of the material.Recently,with the continuous development of lithium resources and its rising price,Na-ion battery?NIB?and K-ion battery?KIB?systems have attracted much attention and are expected to replace LIBs as they operate using similar mechanism,while Na and K are more abundant than Li.However,further development of all such battery systems requires the development of high-capacity anode materials.The research results of this work are as follows:?1?We present a new selective dissolution-regrowth strategy.First,two vanadium matrix composites?FeVO₄ and Cu₃?VO₄?₂?were briefly investigated.FeVO₄nanowires were processed by this strategy to obtain self-assembled hierarchical nanotubes,and Cu₃?VO₄?₂ nanowires were processed by this strategy to obtain self-assembled hierarchical nanowires.We preliminarily prove that this method can construct hierarchical nanostructures.?2?A facile selective dissolution strategy was utilized to produce ultra-thin nanosheet-assembled hierarchical Mn₃O₄/graphene microflowers?Mn₃O₄-G?.The structure evolution during the dissolution process was investigated and the synthetic mechanism was demonstrated as the selective dissolution of vanadium.Benefiting from the ultra-thin nanosheet-assembled hierarchical structure and graphene decoration,the Mn₃O₄-G displayed high lithium storage capacity(about 900 mAh g^-1) and outstanding cycling performance(⁴00 mAh g^-1 after 500 cycles).?3?Since Mn₃O₄ as the anode electrode of sodium ion battery is rarely studied,and it has not been reported as potassium ion battery anode.In addition,when evaluated as NIB anode,the reversible capacity of about 200 mAh g^-1 was attained,which remained at 167 mAh g^-1 after 200 cycles.Moreover,to the best of our knowledge,the potassium storage properties of Mn₃O₄ were evaluated for the first time and a reversible capacity of about 180 mAh g^-1 was achieved.